Docs in progress for ‘QGIS testing’. Visit https://docs.qgis.org/2.18 for QGIS 2.18 docs and translations.

The Vector Properties Dialog

The Layer Properties dialog for a vector layer provides general settings to manage appearance of layer features in the map (symbology, labeling, diagrams), interaction with the mouse (actions, map tips, form design). It also provides information about the layer.

To access the Layer Properties dialog:

  • In the Layers panel, double-click the layer or right-click and select Properties… from the pop-up menu;
  • Go to Layer ‣ Properties… menu when the layer is selected.

The vector Layer Properties dialog provides the following sections:

Tip

Share full or partial properties of the layer styles

The Style menu at the bottom of the dialog allows you to import or export these or part of these properties from/to several destination (file, clipboard, database). See Managing Custom Styles.

Note

Because properties (symbology, label, actions, default values, forms…) of embedded layers (see Nesting Projects) are pulled from the original project file and to avoid changes that may break this behavior, the layer properties dialog is made unavailable for these layers.

Information Properties

metadata The Information tab is read-only and represents an interesting place to quickly grab summarized information and metadata on the current layer. Provided information are:

  • based on the provider of the layer (format of storage, path, geometry type, data source encoding, extent…);
  • picked from the filled metadata (access, links, contacts, history…);
  • or related to its geometry (spatial extent, CRS…) or its attributes (number of fields, characteristics of each…).

Source Properties

system Use this tab to define general settings for the vector layer.

../../../_images/vector_source_menu.png

Source tab in vector Layer Properties dialog

Other than setting the Layer name to display in the Layers Panel, available options include:

Coordinate Reference System

  • Displays the layer’s Coordinate Reference System (CRS) as a PROJ.4 string. You can change the layer’s CRS, selecting a recently used one in the drop-down list or clicking on setProjection Select CRS button (see Coordinate Reference System Selector). Use this process only if the CRS applied to the layer is a wrong one or if none was applied. If you wish to reproject your data into another CRS, rather use layer reprojection algorithms from Processing or Save it into another layer.
  • Create spatial index (only for OGR-supported formats).
  • Update extents information for a layer.

Query Builder

The Query Builder dialog is accessible through the eponym button at the bottom of the Source tab in the Layer Properties dialog, under the Provider feature filter group.

The Query Builder provides an interface that allows you to define a subset of the features in the layer using a SQL-like WHERE clause and to display the result in the main window. As long as the query is active, only the features corresponding to its result are available in the project. For example, using the TYPE_2 field of the regions layer from the QGIS sample data, you could constrain the file to display only regions that are of borough type in the project (see Figure_vector_querybuilder for such an example). The filter is made at the data provider (OGR, PostgreSQL, MSSQL…) level.

../../../_images/queryBuilder.png

Query Builder

You can also open the Query Builder dialog using the Filter… option from the View menu or the layer contextual menu. The Fields, Values and Operators sections in the dialog help you to construct the SQL-like query exposed in the Provider specific filter expression box.

The Fields list contains all the fields of the layer. To add an attribute column to the SQL WHERE clause field, double-click its name or just type it into the SQL box.

The Values frame lists the values of the currently selected field. To list all unique values of a field, click the All button. To instead list the first 25 unique values of the column, click the Sample button. To add a value to the SQL WHERE clause field, double click its name in the Values list. You can use the search box at the top of the Values frame to easily browse and find attribute values in the list.

The Operators section contains all usable operators. To add an operator to the SQL WHERE clause field, click the appropriate button. Relational operators ( = , > , …), string comparison operator (LIKE), and logical operators (AND, OR, …) are available.

The Test button helps you check your query and displays a message box with the number of features satisfying the current query. Use the Clear button to wipe the SQL query and revert the layer to its original state (ie, fully load all the features).

When a filter is applied, QGIS treats the resulting subset acts as if it were the entire layer. For example if you applied the filter above for ‘Borough’ ("TYPE_2" = 'Borough'), you can not display, query, save or edit Anchorage, because that is a ‘Municipality’ and therefore not part of the subset.

Tip

Filtered layers are indicated in the Layers Panel

In the Layers panel, filtered layer is listed with a indicatorFilter Filter icon next to it indicating the query used when the mouse hovers over the button. Double-click the icon opens the Query Builder dialog for edit.

Symbology Properties

symbology The Symbology tab provides you with a comprehensive tool for rendering and symbolizing your vector data. You can use tools that are common to all vector data, as well as special symbolizing tools that were designed for the different kinds of vector data. However all types share the following dialog structure: in the upper part, you have a widget that helps you prepare the classification and the symbol to use for features and at the bottom the Layer rendering widget.

Tip

Switch quickly between different layer representations

Using the Styles ‣ Add menu at the bottom of the Layer Properties dialog, you can save as many styles as needed. A style is the combination of all properties of a layer (such as symbology, labeling, diagram, fields form, actions…) as you want. Then, simply switch between styles from the context menu of the layer in Layers Panel to automatically get different representations of your data.

Tip

Export vector symbology

You have the option to export vector symbology from QGIS into Google *.kml, *.dxf and MapInfo *.tab files. Just open the right mouse menu of the layer and click on Save As… to specify the name of the output file and its format. In the dialog, use the Symbology export menu to save the symbology either as Feature symbology ‣ or as Symbol layer symbology ‣. If you have used symbol layers, it is recommended to use the second setting.

Features rendering

The renderer is responsible for drawing a feature together with the correct symbol. Regardless layer geometry type, there are four common types of renderers: single symbol, categorized, graduated and rule-based. For point layers, there are a point displacement and a heatmap renderers available while polygon layers can also be rendered with the inverted polygons and 2.5 D renderers.

There is no continuous color renderer, because it is in fact only a special case of the graduated renderer. The categorized and graduated renderers can be created by specifying a symbol and a color ramp - they will set the colors for symbols appropriately. For each data type (points, lines and polygons), vector symbol layer types are available. Depending on the chosen renderer, the dialog provides different additional sections.

Note

If you change the renderer type when setting the style of a vector layer the settings you made for the symbol will be maintained. Be aware that this procedure only works for one change. If you repeat changing the renderer type the settings for the symbol will get lost.

Single Symbol Renderer

The singleSymbol Single Symbol renderer is used to render all features of the layer using a single user-defined symbol. See The Symbol Selector for further information about symbol representation.

../../../_images/singlesymbol_ng_line.png

Single symbol line properties

Tip

Edit symbol directly from layer panel

If in your Layers Panel you have layers with categories defined through categorized, graduated or rule-based symbology mode, you can quickly change the fill color of the symbol of the categories by right-clicking on a category and choose the color you prefer from a colorWheel color wheel menu. Right-clicking on a category will also give you access to the options Hide all items, Show all items and Edit symbol.

No Symbols Renderer

The nullSymbol No Symbols renderer is a special use case of the Single Symbol renderer as it applies the same rendering to all features. Using this renderer, no symbol will be drawn for features, but labeling, diagrams and other non-symbol parts will still be shown.

Selections can still be made on the layer in the canvas and selected features will be rendered with a default symbol. Features being edited will also be shown.

This is intended as a handy shortcut for layers which you only want to show labels or diagrams for, and avoids the need to render symbols with totally transparent fill/border to achieve this.

Categorized Renderer

The categorizedSymbol Categorized renderer is used to render the features of a layer, using a user-defined symbol whose aspect reflects the discrete values of a field or an expression. The Categorized menu allows you to

  • select an existing field (using the Column listbox) or

  • type or build an expression using the expression Set column expression. The expression used to classify features can be of any type; it can for example:

    • be a comparison, e.g. myfield >= 100, $id = @atlas_featureid, myfield % 2 = 0, within( $geometry, @atlas_geometry ). In this case, QGIS returns values 1 (True) and 0 (False).

    • combine different fields, e.g. concat( field1, ' ', field2 ) particularly useful when you want to process classification on two or more fields simultaneously.

    • be a calculation on fields, e.g. myfield % 2, year( myfield ) field_1 + field_2.

    • be used to transform linear values in discrete classes, e.g.:

      CASE WHEN x > 1000 THEN 'Big' ELSE 'Small' END
      
    • combine several discrete values in one single category, e.g.:

      CASE
      WHEN building IN ('residence', 'mobile home') THEN 'residential'
      WHEN building IN ('commercial', 'industrial') THEN 'Commercial and Industrial'
      END
      

    Note

    While you can use any kind of expression to categorize features, for some complex expressions it might be simpler to use rule-based rendering.

  • the symbol (using the The Symbol Selector dialog) which will be used as base symbol for each class;

  • the range of colors (using the Color ramp listbox) from which color applied to the symbol is selected.

Then click on Classify button to create classes from the distinct value of the attribute column. Each class can be disabled unchecking the checkbox at the left of the class name.

To change symbol, value and/or label of the class, just double click on the item you want to change.

Right-click shows a contextual menu to Copy/Paste, Change color, Change transparency, Change output unit, Change symbol width.

The example in figure_categorized_symbology shows the category rendering dialog used for the rivers layer of the QGIS sample dataset.

../../../_images/categorysymbol_ng_line.png

Categorized Symbolizing options

Tip

Select and change multiple symbols

The Symbology allows you to select multiple symbols and right click to change color, transparency, size, or width of selected entries.

Tip

Match categories to symbol name

In the [Advanced] menu, under the classes, you can choose one of the two first actions to match symbol name to a category name in your classification. Matched to saved symbols match category name with a symbol name from your Style Manager. Match to symbols from file match category name to a symbol name from an external file.

Graduated Renderer

The graduatedSymbol Graduated renderer is used to render all the features from a layer, using an user-defined symbol whose color or size reflects the assignment of a selected feature’s attribute to a class.

Like the Categorized Renderer, the Graduated Renderer allows you to define rotation and size scale from specified columns.

Also, analogous to the Categorized Renderer, it allows you to select:

  • The attribute (using the Column listbox or the expression Set column expression function)
  • The symbol (using the Symbol selector dialog)
  • The legend format and the precision
  • The method to use to change the symbol: color or size
  • The colors (using the color Ramp list) if the color method is selected
  • The size (using the size domain and its unit)

Then you can use the Histogram tab which shows an interactive histogram of the values from the assigned field or expression. Class breaks can be moved or added using the histogram widget.

Note

You can use Statistical Summary panel to get more information on your vector layer. See Statistical Summary Panel.

Back to the Classes tab, you can specify the number of classes and also the mode for classifying features within the classes (using the Mode list). The available modes are:

  • Equal Interval: each class has the same size (e.g. values from 0 to 16 and 4 classes, each class has a size of 4).
  • Quantile: each class will have the same number of element inside (the idea of a boxplot).
  • Natural Breaks (Jenks): the variance within each class is minimal while the variance between classes is maximal.
  • Standard Deviation: classes are built depending on the standard deviation of the values.
  • Pretty Breaks: Computes a sequence of about n+1 equally spaced nice values which cover the range of the values in x. The values are chosen so that they are 1, 2 or 5 times a power of 10. (based on pretty from the R statistical environment http://astrostatistics.psu.edu/datasets/R/html/base/html/pretty.html)

The listbox in the center part of the Symbology tab lists the classes together with their ranges, labels and symbols that will be rendered.

Click on Classify button to create classes using the chosen mode. Each classes can be disabled unchecking the checkbox at the left of the class name.

To change symbol, value and/or label of the class, just double click on the item you want to change.

Right-click shows a contextual menu to Copy/Paste, Change color, Change transparency, Change output unit, Change symbol width.

The example in figure_graduated_symbology shows the graduated rendering dialog for the rivers layer of the QGIS sample dataset.

../../../_images/graduatesymbol_ng_line.png

Graduated Symbolizing options

Tip

Thematic maps using an expression

Categorized and graduated thematic maps can be created using the result of an expression. In the properties dialog for vector layers, the attribute chooser is extended with a expression Set column expression function. So you don’t need to write the classification attribute to a new column in your attribute table if you want the classification attribute to be a composite of multiple fields, or a formula of some sort.

Proportional Symbol and Multivariate Analysis

Proportional Symbol and Multivariate Analysis are not rendering types available from the Symbology rendering drop-down list. However with the data-defined override options applied over any of the previous rendering options, QGIS allows you to display your point and line data with such representation.

Creating proportional symbol

To apply a proportional rendering:

  1. First apply to the layer the single symbol renderer.

  2. Then set the symbol to apply to the features.

  3. Select the item at the upper level of the symbol tree, and use the dataDefined Data-defined override button next to the Size (for point layer) or Width (for line layer) option.

  4. Select a field or enter an expression, and for each feature, QGIS will apply the output value to the property and proportionally resize the symbol in the map canvas.

    If need be, use the Size assistant… option of the dataDefined menu to apply some transformation (exponential, flannery…) to the symbol size rescaling (see Using the data-defined assistant interface for more details).

You can choose to display the proportional symbols in the Layers panel and the print layout legend item: unfold the Advanced drop-down list at the bottom of the main dialog of the Symbology tab and select Data-defined size legend… to configure the legend items (see Data-defined size legend for details).

../../../_images/proportional_symbols.png

Scaling airports size based on number of passengers

Creating multivariate analysis

A multivariate analysis rendering helps you evaluate the relationship between two or more variables e.g., one can be represented by a color ramp while the other is represented by a size.

The simplest way to create multivariate analysis in QGIS is to:

  1. First apply a categorized or graduated rendering on a layer, using the same type of symbol for all the classes.
  2. Then, apply a proportional symbology on the classes:
    1. Click on the Change button above the classification frame: you get the The Symbol Selector dialog.
    2. Rescale the size or width of the symbol layer using the dataDefined data defined override widget as seen above.

Like the proportional symbol, the scaled symbology can be added to the layer tree, on top of the categorized or graduated classes symbols using the :ref:` data defined size legend <size data_defined_size_legend>` feature. And both representation are also available in the print layout legend item.

../../../_images/multivariate_example.png

Multivariate example with scaled size legend

Tip

Add the size scaled symbols to the print layout legend

Rule-based Renderer

The ruleBasedSymbol Rule-based renderer is used to render all the features from a layer, using rule-based symbols whose aspect reflects the assignment of a selected feature’s attribute to a class. The rules are based on SQL statements and can be nested. The dialog allows rule grouping by filter or scale, and you can decide if you want to enable symbol levels or use only the first-matched rule.

To create a rule:

  1. Activate an existing row by double-clicking it (by default, QGIS adds a symbol without a rule when the rendering mode is enabled) or click the projectProperties Edit rule or signPlus Add rule button.
  2. In the Edit Rule dialog that opens, you can define a label to help you identify each rule. This is the label that will be displayed in the Layers Panel and also in the print composer legend.
  3. Manually enter an expression in the text box next to the radioButtonOn Filter option or press the expression button next to it to open the expression string builder dialog.
  4. Use the provided functions and the layer attributes to build an expression to filter the features you’d like to retrieve. Press the Test button to check the result of the query.
  5. You can enter a longer label to complete the rule description.
  6. You can use the checkbox Scale Range option to set scales at which the rule should be applied.
  7. Finally, configure the symbol to use for these features.
  8. And press OK.

A new row summarizing the rule is added to the Layer Properties dialog. You can create as many rules as necessary following the steps above or copy pasting an existing rule. Drag-and-drop the rules on top of each other to nest them and refine the upper rule features in subclasses.

Selecting a rule, you can also organize its features in subclasses using the Refine selected rules drop-down menu. Automated rule refinement can be based on:

Refined classes appear like sub-items of the rule, in a tree hierarchy and like above, you can set symbology of each class.

In the Edit rule dialog, you can avoid writing all the rules and make use of the radioButtonOff Else option to catch all the features that do not match any of the other rules, at the same level. This can also be achieved by writing Else in the Rule column of the Layer Properties ‣ Symbology ‣ Rule-based dialog.

The created rules also appear in a tree hierarchy in the map legend. Double-click the rules in the map legend and the Symbology tab of the layer properties appears showing the rule that is the background for the symbol in the tree.

The example in figure_rule_based_symbology shows the rule-based rendering dialog for the rivers layer of the QGIS sample dataset.

../../../_images/rulesymbol_ng_line.png

Rule-based Symbolizing options

Point displacement Renderer

The pointDisplacementSymbol Point Displacement renderer works to visualize all features of a point layer, even if they have the same location. To do this, the renderer takes the points falling in a given Distance tolerance from each other and places them around their barycenter following different Placement methods:

  • Ring: places all the features on a circle whose radius depends on the number of features to display.
  • Concentric rings: uses a set of concentric circles to show the features.
  • Grid: generates a regular grid with a point symbol at each intersection.

The Center symbol widget helps you customize the symbol and color of the middle point. For the distributed points symbols, you can apply any of the No symbols, Single symbol, Categorized, Graduated or Rule-based renderer using the Renderer drop-down list and customize them using the Renderer Settings… button.

While the minimal spacing of the Displacement lines depends on the point symbol renderer’s, you can still customize some of its settings such as the Stroke width, Stroke color and Size adjustment (eg, to add more spacing between the rendered points).

Use the Labels group options to perform points labeling: the labels are placed near the displaced position of the symbol, and not at the feature real position. Other than the Label attribute, Label font and Label color, you can set the Minimum map scale to display the labels.

../../../_images/poi_displacement.png

Point displacement dialog

Note

Point Displacement renderer does not alter feature geometry, meaning that points are not moved from their position. They are still located at their initial place. Changes are only visual, for rendering purpose. Use instead the Processing Points displacement algorithm if you want to create displaced features.

Point Cluster Renderer

Unlike the pointDisplacementSymbol Point Displacement renderer which blows up nearest or overlaid point features placement, the pointClusterSymbol Point Cluster renderer groups nearby points into a single rendered marker symbol. Based on a specified Distance, points that fall within from each others are merged into a single symbol. Points aggregation is made based on the closest group being formed, rather than just assigning them the first group within the search distance.

From the main dialog, you can:

  • set the symbol to represent the point cluster in the Cluster symbol; the default rendering displays the number of aggregated features thanks to the @cluster_size variable on Font marker symbol layer.
  • use the Renderer drop-down list to apply any of the other feature rendering types to the layer (single, categorized, rule-based…). Then, push the Renderer Settings… button to configure features’ symbology as usual. Note that this renderer is only visible on features that are not clustered. Also, when the symbol color is the same for all the point features inside a cluster, that color sets the @cluster_color variable of the cluster.
../../../_images/cluster_symbol.png

Point Cluster dialog

Note

Point Cluster renderer does not alter feature geometry, meaning that points are not moved from their position. They are still located at their initial place. Changes are only visual, for rendering purpose. Use instead the Processing K-means clustering NEW in 3.4 or DBSCAN clustering NEW in 3.4 algorithm if you want to create cluster-based features.

Inverted Polygon Renderer

The invertedSymbol Inverted Polygon renderer allows user to define a symbol to fill in outside of the layer’s polygons. As above you can select subrenderers, namely Single symbol, Graduated, Categorized, Rule-Based or 2.5D renderer.

../../../_images/inverted_polygon_symbol.png

Inverted Polygon dialog

Heatmap Renderer

With the heatmapSymbol Heatmap renderer you can create live dynamic heatmaps for (multi)point layers. You can specify the heatmap radius in pixels, mm or map units, choose and edit a color ramp for the heatmap style and use a slider for selecting a trade-off between render speed and quality. You can also define a maximum value limit and give a weight to points using a field or an expression. When adding or removing a feature the heatmap renderer updates the heatmap style automatically.

../../../_images/heatmap_symbol.png

Heatmap dialog

2.5D Renderer

Using the 25dSymbol 2.5D renderer it’s possible to create a 2.5D effect on your layer’s features. You start by choosing a Height value (in map units). For that you can use a fixed value, one of your layer’s fields, or an expression. You also need to choose an Angle (in degrees) to recreate the viewer position (0° means west, growing in counter clock wise). Use advanced configuration options to set the Roof Color and Wall Color. If you would like to simulate solar radiation on the features walls, make sure to check the checkbox Shade walls based on aspect option. You can also simulate a shadow by setting a Color and Size (in map units).

../../../_images/2_5dsymbol.png

2.5D dialog

Tip

Using 2.5D effect with other renderers

Once you have finished setting the basic style on the 2.5D renderer, you can convert this to another renderer (single, categorized, graduated). The 2.5D effects will be kept and all other renderer specific options will be available for you to fine tune them (this way you can have for example categorized symbols with a nice 2.5D representation or add some extra styling to your 2.5D symbols). To make sure that the shadow and the “building” itself do not interfere with other nearby features, you may need to enable Symbols Levels ( Advanced ‣ Symbol levels…). The 2.5D height and angle values are saved in the layer’s variables, so you can edit it afterwards in the variables tab of the layer’s properties dialog.

Layer rendering

From the Symbology tab, you can also set some options that invariably act on all features of the layer:

  • Opacity slider: You can make the underlying layer in the map canvas visible with this tool. Use the slider to adapt the visibility of your vector layer to your needs. You can also make a precise definition of the percentage of visibility in the the menu beside the slider.

  • Blending mode at the Layer and Feature levels: You can achieve special rendering effects with these tools that you may previously only know from graphics programs. The pixels of your overlaying and underlaying layers are mixed through the settings described in Blending Modes.

  • Apply paint effects on all the layer features with the Draw Effects button.

  • Control feature rendering order allows you, using features attributes, to define the z-order in which they shall be rendered. Activate the checkbox and click on the sort button beside. You then get the Define Order dialog in which you:

    1. Choose a field or build an expression to apply to the layer features.
    2. Set in which order the fetched features should be sorted, i.e. if you choose Ascending order, the features with lower value are rendered under those with higher value.
    3. Define when features returning NULL value should be rendered: first (bottom) or last (top).
    4. Repeat the above steps as many times as rules you wish to use.

    The first rule is applied to all the features in the layer, z-ordering them according to their returned value. Then, within each group of features with the same value (including those with NULL value) and thus the same z-level, the next rule is applied to sort them. And so on…

../../../_images/layer_rendering_options.png

Layer rendering options

Other Settings

Symbol levels

For renderers that allow stacked symbol layers (only heatmap doesn’t) there is an option to control the rendering order of each symbol’s levels.

For most of the renderers, you can access the Symbols levels option by clicking the Advanced button below the saved symbols list and choosing Symbol levels. For the Rule-based Renderer the option is directly available through Symbols Levels… button, while for Point displacement Renderer renderer the same button is inside the Rendering settings dialog.

To activate symbols levels, select the checkbox Enable symbol levels. Each row will show up a small sample of the combined symbol, its label and the individual symbols layer divided into columns with a number next to it. The numbers represent the rendering order level in which the symbol layer will be drawn. Lower values levels are drawn first, staying at the bottom, while higher values are drawn last, on top of the others.

../../../_images/symbol_levels.png

Symbol levels dialog

Note

If symbols levels are deactivated, the complete symbols will be drawn according to their respective features order. Overlapping symbols will simply obfuscate to other below. Besides, similar symbols won’t “merge” with each other.

../../../_images/symbol_levels_examples.png

Symbol levels activated (A) and deactivated (B) difference

Data-defined size legend

When a layer is rendered with the proportional symbol or the multivariate rendering or when a scaled size diagram is applied to the layer, you can allow the display of the scaled symbols in both the Layers panel and the print layout legend.

To enable the Data-defined Size Legend dialog to render symbology, select the eponym option in the Advanced button below the saved symbols list. For diagrams, the option is available under the Legend tab. The dialog provides the following options to:

  • select the type of legend: radioButtonOn Legend not enabled, radioButtonOff Separated legend items and radioButtonOff Collapsed legend. For the latter option, you can select whether the legend items are aligned at the Bottom or at the Center;
  • set the symbol to use for legend representation;
  • insert the title in the legend;
  • resize the classes to use: by default, QGIS provides you with a legend of five classes (based on natural pretty breaks) but you can apply your own classification using the checkbox Manual size classes option. Use the signPlus and signMinus buttons to set your custom classes values and labels.

A preview of the legend is displayed in the right panel of the dialog and updated as you set the parameters. For collapsed legend, a leader line from the horizontal center of the symbol to the corresponding legend text is drawn.

../../../_images/data_defined_size_legend.png

Setting size scaled legend

Note

Currently, data-defined size legend for layer symbology can only be applied to point layer using single, categorized or graduated symbology.

Draw effects

In order to improve layer rendering and avoid (or at least reduce) the resort to other software for final rendering of maps, QGIS provides another powerful functionality: the paintEffects Draw Effects options, which adds paint effects for customizing the visualization of vector layers.

The option is available in the Layer Properties –> Symbology dialog, under the Layer rendering group (applying to the whole layer) or in symbol layer properties (applying to corresponding features). You can combine both usage.

Paint effects can be activated by checking the checkbox Draw effects option and clicking the paintEffects Customize effects button, that will open the Effect Properties Dialog (see figure_effects_source). The following effect types, with custom options are available:

  • Source: Draws the feature’s original style according to the configuration of the layer’s properties. The transparency of its style can be adjusted.

    ../../../_images/source.png

    Draw Effects: Source dialog

  • Blur: Adds a blur effect on the vector layer. The options that someone can change are the Blur type (Stack or Gaussian blur), the strength and transparency of the blur effect.

    ../../../_images/blur.png

    Draw Effects: Blur dialog

  • Colorize: This effect can be used to make a version of the style using one single hue. The base will always be a grayscale version of the symbol and you can use the selectString Grayscale to select how to create it (options are: ‘lightness’, ‘luminosity’ and ‘average’). If checkbox Colorise is selected, it will be possible to mix another color and choose how strong it should be. You can also control the Brightness, contrast and saturation levels of the resulting symbol.

    ../../../_images/colorise.png

    Draw Effects: Colorize dialog

  • Drop Shadow: Using this effect adds a shadow on the feature, which looks like adding an extra dimension. This effect can be customized by changing the offset degrees and radius, determining where the shadow shifts towards to and the proximity to the source object. Drop Shadow also has the option to change the blur radius, the transparency and the color of the effect.

    ../../../_images/drop_shadow.png

    Draw Effects: Drop Shadow dialog

  • Inner Shadow: This effect is similar to the Drop Shadow effect, but it adds the shadow effect on the inside of the edges of the feature. The available options for customization are the same as the Drop Shadow effect.

    ../../../_images/inner_shadow.png

    Draw Effects: Inner Shadow dialog

  • Inner Glow: Adds a glow effect inside the feature. This effect can be customized by adjusting the spread (width) of the glow, or the Blur radius. The latter specifies the proximity from the edge of the feature where you want any blurring to happen. Additionally, there are options to customize the color of the glow, with a single color or a color ramp.

    ../../../_images/inner_glow.png

    Draw Effects: Inner Glow dialog

  • Outer Glow: This effect is similar to the Inner Glow effect, but it adds the glow effect on the outside of the edges of the feature. The available options for customization are the same as the Inner Glow effect.

    ../../../_images/outer_glow.png

    Draw Effects: Outer Glow dialog

  • Transform: Adds the possibility of transforming the shape of the symbol. The first options available for customization are the Reflect horizontal and Reflect vertical, which actually create a reflection on the horizontal and/or vertical axes. The 4 other options are:

    • Shear: slants the feature along the x and/or y axis
    • Scale: enlarges or minimizes the feature along the x and/or y axis by the given percentage
    • Rotation: turns the feature around its center point
    • and Translate changes the position of the item based on a distance given on the x and/or the y axis.
    ../../../_images/transform.png

    Draw Effects: Transform dialog

There are some common options available for all draw effect types. Transparency and Blend mode options work similar to the ones described in Layer rendering and can be used in all draw effects except for the transform one.

One or more draw effects can used at the same time. You activate/deactivate an effect using its checkbox in the effects list. You can change the selected effect type by using the selectString Effect type option. You can reorder the effects using arrowUp Move up and arrowDown Move down buttons, and also add/remove effects using the signPlus Add effect and signMinus Remove effect buttons.

There is also a selectString Draw mode option available for every draw effect, and you can choose whether to render and/or to modify the symbol. Effects render from top to bottom.’Render only’ mode means that the effect will be visible while the ‘Modify only’ mode means that the effect will not be visible but the changes that it applies will be passed to the next effect (the one immediately below). The ‘Render and Modify’ mode will make the effect visible and pass any changes to the next effect. If the effect is in the top of the effects list or if the immediately above effect is not in modify mode, then it will use the original source symbol from the layers properties (similar to source).

Labels Properties

The labeling Labels properties provides you with all the needed and appropriate capabilities to configure smart labeling on vector layers. This dialog can also be accessed from the Layer Styling panel, or using the labeling Layer Labeling Options icon of the Labels toolbar.

The first step is to choose the labeling method from the drop-down list. Available methods are:

  • labelingNone No labels: the default value, showing no labels from the layer
  • labeling Single labels, described below
  • labelingRuleBased Rule-based labeling
  • and labelingObstacle Blocking: allows to set a layer as just an obstacle for other layer’s labels without rendering any labels of its own.

Setting a label

The next steps assume you select the labeling Single labels option, enabling following tabs that help you configure the labeling:

It also enables the Label with drop-down list, from which you can select an attribute column to use. Click expression if you want to define labels based on expressions - See Define labels based on expressions.

The following steps describe simple labeling without using the Data defined override functions, which are situated next to the drop-down menus - see Using data-defined override for labeling for a use case.

../../../_images/label_menu_text.png

Layer labeling settings - Text tab

Text tab

In the text Text tab, you can define the Font, Style, and Size of your labels’ text (see Figure_labels). There are options available to set the labels’ Color and Transparency. Use the Type case option to change the capitalization style of the text. You have the possibility to render the text as ‘All uppercase’, ‘All lowercase’ or ‘Capitalize first letter’. In Spacing, you can change the space between words and between individual letters. Finally, use the Blend mode option to determine how your labels will mix with the map features below them (see more about it in Blending Modes).

The Apply label text substitutes option gives you ability to specify a list of texts to substitute to texts in feature labels (e.g., abbreviating street types). Replacement texts are thus used to display labels in the map canvas. Users can also export and import lists of substitutes to make reuse and sharing easier.

Formatting tab

In the labelformatting Formatting tab, you can define a character for a line break in the labels with the Wrap on character option. You can also format the Line Height and the alignment. For the latter, typical values are available (left, right, and center), plus Follow label placement for point layers. When set to this mode, text alignment for labels will be dependent on the final placement of the label relative to the point. E.g., if the label is placed to the left of the point, then the label will be right aligned, while if it is placed to the right, it will be left aligned.

For line vector layers you can include Line directions symbols to help determine the lines directions. They work particularly well when used with the curved or Parallel placement options from the Placement tab. There are options to set the symbols position, and to reverse direction.

Use the checkbox Formatted numbers option to format numeric labels. You can set the number of Decimal places. By default, 3 decimal places will be used. Use the checkbox Show plus sign if you want to show the plus sign in positive numbers.

Buffer tab

To create a buffer around the labels, activate the checkbox Draw text buffer checkbox in the labelbuffer Buffer tab. You can set the buffer’s Size, color, and Transparency. The buffer expands from the label’s outline , so, if the checkbox color buffer’s fill checkbox is activated, the buffer interior is filled. This may be relevant when using partially transparent labels or with non-normal blending modes, which will allow seeing behind the label’s text. Deactivating checkbox color buffer’s fill checkbox (while using totally transparent labels) will allow you to create outlined text labels.

Background tab

In the labelbackground Background tab, you can define with Size X and Size Y the shape of your background. Use Size type to insert an additional ‘Buffer’ into your background. The buffer size is set by default here. The background then consists of the buffer plus the background in Size X and Size Y. You can set a Rotation where you can choose between ‘Sync with label’, ‘Offset of label’ and ‘Fixed’. Using ‘Offset of label’ and ‘Fixed’, you can rotate the background. Define an Offset X,Y with X and Y values, and the background will be shifted. When applying Radius X,Y, the background gets rounded corners. Again, it is possible to mix the background with the underlying layers in the map canvas using the Blend mode (see Blending Modes).

Shadow tab

Use the labelshadow Shadow tab for a user-defined Draw drop shadow. The drawing of the background is very variable. Choose between ‘Lowest label component’, ‘Text’, ‘Buffer’ and ‘Background’. The Offset angle depends on the orientation of the label. If you choose the checkbox Use global shadow checkbox, then the zero point of the angle is always oriented to the north and doesn’t depend on the orientation of the label. You can influence the appearance of the shadow with the Blur radius. The higher the number, the softer the shadows. The appearance of the drop shadow can also be altered by choosing a blend mode.

Placement tab

Choose the labelplacement Placement tab for configuring label placement and labeling priority. Note that the placement options differ according to the type of vector layer, namely point, line or polygon, and are affected by the global PAL setting.

Placement for point layers

With the radioButtonOn Cartographic placement mode, point labels are generated with a better visual relationship with the point feature, following ideal cartographic placement rules. Labels can be placed at a set Distance either from the point feature itself or from the bounds of the symbol used to represent the feature. The latter option is especially useful when the symbol size isn’t fixed, e.g. if it’s set by a data defined size or when using different symbols in a categorized renderer.

By default, placements are prioritised in the following order:

  1. top right
  2. top left
  3. bottom right
  4. bottom left
  5. middle right
  6. middle left
  7. top, slightly right
  8. bottom, slightly left.

Placement priority can, however, be customized or set for an individual feature using a data defined list of prioritised positions. This also allows only certain placements to be used, so e.g. for coastal features you can prevent labels being placed over the land.

The radioButtonOn Around point setting places the label in an equal radius (set in Distance) circle around the feature. The placement of the label can even be constrained using the Quadrant option.

With the radioButtonOn Offset from point, labels are placed at a fixed offset from the point feature. You can select the Quadrant in which to place your label. You are also able to set the Offset X,Y distances between the points and their labels and can alter the angle of the label placement with the Rotation setting. Thus, placement in a selected quadrant with a defined rotation is possible.

Placement for line layers

Label options for line layers include radioButtonOn Parallel, radioButtonOff Curved or radioButtonOff Horizontal. For the radioButtonOn Parallel and radioButtonOff Curved options, you can set the position to checkbox Above line, checkbox On line and checkbox Below line. It’s possible to select several options at once. In that case, QGIS will look for the optimal label position. For Parallel and curved placement options, you can also use the line orientation for the position of the label. Additionally, you can define a Maximum angle between curved characters when selecting the radioButtonOff Curved option (see Figure_labels_placement_line).

../../../_images/line_label_placement.png

Label placement examples in lines

For all three placement options, in Repeat, you can set up a minimum distance for repeating labels. The distance can be in mm or in map units.

Placement for polygon layers

You can choose one of the following options for placing labels in polygons (see figure_labels_placement_polygon):

  • radioButtonOn Offset from centroid,
  • radioButtonOff Horizontal (slow),
  • radioButtonOff Around centroid,
  • radioButtonOff Free (slow),
  • radioButtonOff Using perimeter,
  • and radioButtonOff Using perimeter (curved).

In the Offset from centroid settings you can specify if the centroid is of the radioButtonOn visible polygon or radioButtonOff whole polygon. That means that either the centroid is used for the polygon you can see on the map or the centroid is determined for the whole polygon, no matter if you can see the whole feature on the map. You can place your label within a specific quadrant, and define offset and rotation.

The Around centroid setting places the label at a specified distance around the centroid. Again, you can define radioButtonOn visible polygon or radioButtonOff whole polygon for the centroid.

With the Horizontal (slow) or Free (slow) options, QGIS places at the best position either a horizontal or a rotated label inside the polygon.

With the Using perimeter option, the label will be drawn next to the polygon boundary. The label will behave like the parallel option for lines. You can define a position and a distance for the label. For the position, checkbox Above line, checkbox On line, checkbox Below line and checkbox Line orientation dependent position are possible. You can specify the distance between the label and the polygon outline, as well as the repeat interval for the label.

The Using perimeter (curved) option helps you draw the label along the polygon boundary, using a curved labeling. In addition to the parameters available with Using perimeter setting, you can set the Maximum angle between curved characters polygon, either inside or outside.

../../../_images/polygon_label_placement.png

Label placement examples in polygons

In the priority section you can define the priority with which labels are rendered for all three vector layer types (point, line, polygon). This placement option interacts with the labels from other vector layers in the map canvas. If there are labels from different layers in the same location, the label with the higher priority will be displayed and the others will be left out.

Rendering tab

In the render Rendering tab, you can tune when the labels can be rendered and their interaction with other labels and features.

Under Label options, you find the scale-based and the Pixel size-based visibility settings.

The Label z-index determines the order in which labels are rendered, as well in relation with other feature labels in the layer (using data-defined override expression), as with labels from other layers. Labels with a higher z-index are rendered on top of labels (from any layer) with lower z-index.

Additionally, the logic has been tweaked so that if 2 labels have matching z-indexes, then:

  • if they are from the same layer, the smaller label will be drawn above the larger label
  • if they are from different layers, the labels will be drawn in the same order as their layers themselves (ie respecting the order set in the map legend).

Note that this setting doesn’t make labels to be drawn below the features from other layers, it just controls the order in which labels are drawn on top of all the layer’s features.

While rendering labels and in order to display readable labels, QGIS automatically evaluates the position of the labels and can hide some of them in case of collision. You can however choose to checkbox Show all labels for this layer (including colliding labels) in order to manually fix their placement.

With data-defined expressions in Show label and Always Show you can fine tune which labels should be rendered.

Under Feature options, you can choose to label every part of a multi-part feature and limit the number of features to be labeled. Both line and polygon layers offer the option to set a minimum size for the features to be labeled, using Suppress labeling of features smaller than. For polygon features, you can also filter the labels to show according to whether they completely fit within the feature or not. For line features, you can choose to Merge connected lines to avoid duplicate labels, rendering a quite airy map in conjunction with the Distance or Repeat options in Placement tab.

From the Obstacles frame, you can manage the covering relation between labels and features. Activate the checkbox Discourage labels from covering features option to decide whether features of the layer should act as obstacles for any label (including labels from other features in the same layer). An obstacle is a feature QGIS tries as far as possible to not place labels over. Instead of the whole layer, you can define a subset of features to use as obstacles, using the dataDefined data-defined override control next to the option.

The slider priority control slider for obstacles allows you to make labels prefer to overlap features from certain layers rather than others. A Low weight obstacle priority means that features of the layer are less considered as obstacles and thus more likely to be covered by labels. This priority can also be data-defined, so that within the same layer, certain features are more likely to be covered than others.

For polygon layers, you can choose the type of obstacle features could be by minimising the labels placement:

  • over the feature’s interior: avoids placing labels over the interior of the polygon (prefers placing labels totally outside or just slightly inside the polygon)
  • or over the feature’s boundary: avoids placing labels over boundary of the polygon (prefers placing labels outside or completely inside the polygon). E.g., it can be useful for regional boundary layers, where the features cover an entire area. In this case, it’s impossible to avoid placing labels within these features, and it looks much better to avoid placing them over the boundaries between features.

Setting the automated placement engine

In the top right corner of the Labels tab, you can use the autoPlacement Automated placement settings (applies to all layers) to configure a global and automated behavior of the labels. Clicking the autoPlacement button provides you with the following options:

../../../_images/placement_engine.png

The labels automated placement engine

  • The Search method combobox provides you with different placement methods for finding good placement solutions for point, line and polygon labeling. More details in this article.
  • The Number of candidates controls set how many label placement candidates should be generated for each feature type. The more candidates generated, the better the labeling will be - but at a cost of rendering speed. Smaller number of candidates results in less labels placed but faster redraws.
  • checkbox Draw text as outlines: controls whether text labels are drawn (and exported) as either proper text objects OR as paths only. If they are exported as text objects then they can be edited in external applications (e.g. Inkscape) as normal text. BUT the side effect is that the rendering quality is decreased, AND there’s issues with rendering when certain text settings like buffers are in place. That’s why drawing as outlines is recommended. Note that when exporting a layout to svg there’s actually an override for this setting - so you can leave the project rendering as outlines but for a .svg export export the labels as text.
  • checkbox Show partial labels: controls whether labels which fall partially outside of the map extent should be rendered. If checked, these labels will be shown (when there’s no way to place them fully within the visible area). If unchecked then partial visible labels will be skipped.
  • checkbox show all labels for all layers (i.e. including colliding objects). Note that this option can be also set per layer (see Rendering tab)
  • checkbox show candidates (for debugging): controls whether boxes should be drawn on the map showing all the candidates generated for label placement. Like the label says, it’s useful only for debugging and testing the effect different labeling settings have. This could be handy for a better manual placement with tools from the label toolbar.

Rule-based labeling

With rule-based labeling multiple label configurations can be defined and applied selectively on the base of expression filters and scale range, as in Rule-based rendering.

To create a rule, select the labelingRuleBased Rule-based labeling option in the main drop-down list from the Labels tab and click the signPlus button at the bottom of the dialog. Then fill the new dialog with a description and an expression to filter features. You can also set a scale range in which the label rule should be applied. The other options available in this dialog are the common settings seen beforehand.

../../../_images/label_rule_settings.png

Rule settings

A summary of existing rules is shown in the main dialog (see figure_labels_rule_based). You can add multiple rules, reorder or imbricate them with a drag-and-drop. You can as well remove them with the signMinus button or edit them with projectProperties button or a double-click.

../../../_images/label_rules_panel.png

Rule based labeling panel

Define labels based on expressions

Whether you choose single or rule-based labeling type, QGIS allows using expressions to label features.

Assuming you are using the Single labels method, click the expression icon near the Label with drop-down list in the labeling Labels tab of the properties dialog.

In figure_labels_expression, you see a sample expression to label the alaska regions with name and area size, based on the field ‘NAME_2’, some descriptive text, and the function $area in combination with format_number() to make it look nicer.

../../../_images/label_expression.png

Using expressions for labeling

Expression based labeling is easy to work with. All you have to take care of is that:

  • You may need to combine all elements (strings, fields, and functions) with a string concatenation function such as concat, + or ||. Be aware that in some situations (when null or numeric value are involved) not all of these tools will fit your need.
  • Strings are written in ‘single quotes’.
  • Fields are written in “double quotes” or without any quote.

Let’s have a look at some examples:

  1. Label based on two fields ‘name’ and ‘place’ with a comma as separator:

    "name" || ', ' || "place"
    

    Returns:

    John Smith, Paris
    
  2. Label based on two fields ‘name’ and ‘place’ with other texts:

    'My name is ' + "name" + 'and I live in ' + "place"
    'My name is ' || "name" || 'and I live in ' || "place"
    concat('My name is ', name, ' and I live in ', "place")
    

    Returns:

    My name is John Smith and I live in Paris
    
  3. Label based on two fields ‘name’ and ‘place’ with other texts combining different concatenation functions:

    concat('My name is ', name, ' and I live in ' || place)
    

    Returns:

    My name is John Smith and I live in Paris
    

    Or, if the field ‘place’ is NULL, returns:

    My name is John Smith
    
  4. Multi-line label based on two fields ‘name’ and ‘place’ with a descriptive text:

    concat('My name is ', "name", '\n' , 'I live in ' , "place")
    

    Returns:

    My name is John Smith
    I live in Paris
    
  5. Label based on a field and the $area function to show the place’s name and its rounded area size in a converted unit:

    'The area of ' || "place" || ' has a size of '
    || round($area/10000) || ' ha'
    

    Returns:

    The area of Paris has a size of 10500 ha
    
  6. Create a CASE ELSE condition. If the population value in field population is <= 50000 it is a town, otherwise it is a city:

    concat('This place is a ',
    CASE WHEN "population" <= 50000 THEN 'town' ELSE 'city' END)
    

    Returns:

    This place is a town
    
  7. Display name for the cities and no label for the other features (for the “city” context, see example above):

    CASE WHEN "population" > 50000 THEN "NAME" END
    

    Returns:

    Paris
    

As you can see in the expression builder, you have hundreds of functions available to create simple and very complex expressions to label your data in QGIS. See Expressions chapter for more information and examples on expressions.

Using data-defined override for labeling

With the dataDefined Data defined override function, the settings for the labeling are overridden by entries in the attribute table or expressions based on them. This feature can be used to set values for most of the labeling options described above.

For example, using the Alaska QGIS sample dataset, let’s label the airports layer with their name, based on their militarian USE, i.e. whether the airport is accessible to :

  • military people, then display it in gray color, size 8;
  • others, then show in blue color, size 10.

To do this, after you enabled the labeling on the NAME field of the layer (see Setting a label):

  1. Activate the Text tab.

  2. Click on the dataDefined icon next to the Size property.

  3. Select Edit… and type:

    CASE
      WHEN "USE" like '%Military%' THEN 8 -- because compatible values are 'Military'
                                          -- and 'Joint Military/Civilian'
      ELSE 10
    END
    
  4. Press OK to validate. The dialog closes and the dataDefined button becomes dataDefineExpressionOn meaning that an rule is being run.

  5. Then click the button next to the color property, type the expression below and validate:

    CASE
      WHEN "USE" like '%Military%' THEN '150, 150, 150'
      ELSE '0, 0, 255'
    END
    

Likewise, you can customize any other property of the label, the way you want. See more details on the dataDefined Data-define override widget’s description and manipulation in Data defined override setup section.

../../../_images/label_attribute_data_defined.png

Airports labels are formatted based on their attributes

The Label Toolbar

The Label Toolbar provides some tools to manipulate labeling label or diagram diagram properties, but only if the corresponding data-defined option is indicated (otherwise, buttons are disabled). Layer might also need to be in edit mode.

../../../_images/diagram_toolbar.png

The Label toolbar

While for readability, label has been used below to describe the Label toolbar, note that when mentioned in their name, the tools work almost the same way with diagrams:

  • pinLabels Pin/Unpin Labels And Diagrams that has data-defined position. By clicking or draging an area, you pin label(s). If you click or drag an area holding Shift, label(s) are unpinned. Finally, you can also click or drag an area holding Ctrl to toggle the pin status of label(s).
  • showPinnedLabels Highlight Pinned Labels And Diagrams. If the vector layer of the label is editable, then the highlighting is green, otherwise it’s blue.
  • moveLabel Move Label And Diagram that has data-defined position. You just have to drag the label to the desired place.
  • showHideLabels Show/Hide Labels And Diagrams that has data-defined visbility. If you click or drag an area holding Shift, then label(s) are hidden. When a label is hidden, you just have to click or drag an area around the feature’s point to restore its visibility.
  • rotateLabel Rotate Label. Click the label and move around and you get the text rotated.
  • changeLabelProperties Change Label. It opens a dialog to change the clicked label properties; it can be the label itself, its coordinates, angle, font, size… as long as this property has been mapped to a field.

Warning

Label tools overwrite current field values

Using the Label toolbar to customize the labeling actually writes the new value of the property in the mapped field. Hence, be careful to not inadvertently replace data you may need later!

Note

The Auxiliary Storage Properties mechanism may be used to customize labeling (position, and so on) without modifying the underlying data source.

Customize the labels from the map canvas

Combined with the Label Toolbar, the data defined override setting helps you manipulate labels in the map canvas (move, edit, rotate). We now describe an example using the data-defined override function for the moveLabelMove label function (see figure_labels_coordinate_data_defined).

  1. Import lakes.shp from the QGIS sample dataset.

  2. Double-click the layer to open the Layer Properties. Click on Labels and Placement. Select radioButtonOn Offset from centroid.

  3. Look for the Data defined entries. Click the dataDefined icon to define the field type for the Coordinate. Choose xlabel for X and ylabel for Y. The icons are now highlighted in yellow.

    ../../../_images/label_coordinate_data_defined.png

    Labeling of vector polygon layers with data-defined override

  4. Zoom into a lake.

  5. Set editable the layer using the toggleEditing Toggle Editing button.

  6. Go to the Label toolbar and click the moveLabel icon. Now you can shift the label manually to another position (see figure_labels_move). The new position of the label is saved in the xlabel and ylabel columns of the attribute table.

  7. Using The Geometry Generator with the expression below, you can also add a linestring symbol layer to connect each lake to its moved label:

    make_line( centroid( $geometry ), make_point( "xlabel", "ylabel" ) )
    
    ../../../_images/move_label.png

    Moved labels

Note

The Auxiliary Storage Properties mechanism may be used with data-defined properties without having an editable data source.

Diagrams Properties

diagram The Diagrams tab allows you to add a graphic overlay to a vector layer (see figure_diagrams_attributes).

The current core implementation of diagrams provides support for:

  • diagramNone No diagrams: the default value with no diagram displayed over the features;
  • piechart Pie charts, a circular statistical graphic divided into slices to illustrate numerical proportion. The arc length of each slice is proportional to the quantity it represents;
  • text Text diagrams, a horizontaly divided circle showing statistics values inside;
  • and histogram Histograms.

In the top right corner of the Diagrams tab, the autoPlacement Automated placement settings (applies to all layers) button provides means to control diagram labels placement on the map canvas.

Tip

Switch quickly between types of diagrams

Given that the settings are almost common to the different types of diagram, when designing your diagram, you can easily change the diagram type and check which one is more appropriate to your data without any loss.

For each type of diagram, the properties are divided into several tabs:

Attributes

Attributes defines which variables to display in the diagram. Use signPlus add item button to select the desired fields into the ‘Assigned Attributes’ panel. Generated attributes with Expressions can also be used.

You can move up and down any row with click and drag, sorting how attributes are displayed. You can also change the label in the ‘Legend’ column or the attribute color by double-clicking the item.

This label is the default text displayed in the legend of the print layout or of the layer tree.

../../../_images/diagram_tab.png

Diagram properties - Attributes tab

Rendering

Rendering defines how the diagram looks like. It provides general settings that do not interfere with the statistic values such as:

  • the graphic’s opacity, its outline width and color;
  • and, depending on the type of diagram:
    • the width of the bar in case of histogram;
    • the circle background color in case of text diagram, and the font used for texts;
    • the orientation of the left line of the first slice represented in pie chart. Note that slices are displayed clockwise.

In this tab, you can also manage and fine tune the diagram visibility with different options:

  • Diagram z-index: controls how diagrams are drawn on top of each other and on top of labels. A diagram with a high index is drawn over diagrams and labels;
  • checkbox Show all diagrams: shows all the diagrams even if they overlap each other;
  • Show diagram: allows only specific diagrams to be rendered;
  • Always Show: selects specific diagrams to always render, even when they overlap other diagrams or map labels;
  • setting the Scale dependent visibility;
  • Discourage diagrams and labels from covering features: defines features to use as obstacles, ie QGIS will try to not place diagrams nor labels over these features.
../../../_images/diagram_tab_appearance.png

Diagram properties - Rendering tab

Size

Size is the main tab to set how the selected statistics are represented. The diagram size units can be ‘Map Units’ or ‘Millimeters’. You can use :

  • Fixed size, an unique size to represent the graphic of all the features, except when displaying histogram
  • or Scaled size, based on an expression using layer attributes.
../../../_images/diagram_tab_size.png

Diagram properties - Size tab

Placement

Placement helps to define diagram position. According to the layer geometry type, it offers different options for the placement:

  • ‘Over the point’ or ‘Around the point’ for point geometry. The latter variable requires a radius to follow.
  • ‘Over the line’ or ‘Around the line’ for line geometry. Like point feature, the last variable requires a distance to respect and user can specify the diagram placement relative to the feature (‘above’, ‘on’ and/or ‘below’ the line) It’s possible to select several options at once. In that case, QGIS will look for the optimal position of the diagram. Remember that here you can also use the line orientation for the position of the diagram.
  • ‘Over the centroid’, ‘Around the centroid’ (with a distance set), ‘Perimeter’ and anywhere ‘Inside polygon’ are the options for polygon features.

The diagram can also be placed using feature data to fill the coordinates X and Y fields.

The placement of the diagrams can interact with the labeling, so you can detect and solve position conflicts between diagrams and labels by setting the Priority slider value.

../../../_images/diagram_tab_placement.png

Vector properties dialog with diagram properties, Placement tab

Options

The Options tab has settings only in case of histogram. You can choose whether the bar orientation should be ‘Up’, ‘Down’, ‘Right’ and ‘Left’.

Legend

From the Legend tab, you can choose to display items of the diagram in the Layers Panel, and in the print layout legend, next to the layer symbology:

  • check Show legend entries for diagram attributes to display in the legends the Color and Legend properties, as previously assigned in the Attributes tab;
  • and, when a scaled size is being used for the diagrams, push the Legend Entries for Diagram Size… button to configure the diagram symbol aspect in the legends. This opens the Data-defined Size Legend dialog whose options are described in Data-defined size legend.

When set, the diagram legend items (attributes with color and diagram size) are also displayed in the print layout legend, next to the layer symbology.

Case Study

We will demonstrate an example and overlay on the Alaska boundary layer a text diagram showing temperature data from a climate vector layer. Both vector layers are part of the QGIS sample dataset (see section Downloading sample data).

  1. First, click on the addOgrLayer Load Vector icon, browse to the QGIS sample dataset folder, and load the two vector shape layers alaska.shp and climate.shp.
  2. Double click the climate layer in the map legend to open the Layer Properties dialog.
  3. Click on the Diagrams tab and from the Diagram type selectString combo box, select ‘Text diagram’.
  4. In the Appearance tab, we choose a light blue as background color, and in the Size tab, we set a fixed size to 18 mm.
  5. In the Position tab, placement could be set to ‘Around Point’.
  6. In the diagram, we want to display the values of the three columns T_F_JAN, T_F_JUL and T_F_MEAN. So, in the Attributes tab first select T_F_JAN and click the signPlus button, then repeat with T_F_JUL and finally T_F_MEAN.
  7. Now click Apply to display the diagram in the QGIS main window.
  8. You can adapt the chart size in the Size tab. Activate the radioButtonOn Scaled size and set the size of the diagrams on the basis of the maximum value of an attribute and the Size option. If the diagrams appear too small on the screen, you can activate the checkbox Increase size of small diagrams checkbox and define the minimum size of the diagrams.
  9. Change the attribute colors by double clicking on the color values in the Assigned attributes field. Figure_diagrams_mapped gives an idea of the result.
  10. Finally, click OK.
../../../_images/climate_diagram.png

Diagram from temperature data overlayed on a map

Remember that in the Position tab, a checkbox Data defined position of the diagrams is possible. Here, you can use attributes to define the position of the diagram. You can also set a scale-dependent visibility in the Appearance tab.

The size and the attributes can also be an expression. Use the expression button to add an expression. See Expressions chapter for more information and example.

Using data-defined override

As mentioned above, you can use some custom data-defined to tune the diagrams rendering:

  • position in Placement tab by filling X and Y fields
  • visibility in Appearance tab by filling the Visibility field

See Using data-defined override for labeling for more information.

Source Fields Properties

sourceFields The Source Fields tab provides information on fields related to the layer and helps you organize them.

The layer can be made editable using the toggleEditing Toggle editing mode. At this moment, you can modify its structure using the newAttribute New field and deleteAttribute Delete field buttons.

You can also rename fields by double-clicking its name. This is only supported for data providers like PostgreSQL, Oracle, Memory layer and some OGR layer depending on the OGR data format and version.

You can define some alias to display human readable fields in the feature form or the attribute table. In this case, you don’t need to switch to editing mode. Alias are saved in project file.

Depending on the data provider, you can associate a comment with a field, for example at its creation. This information is retrieved and shown in the Comment column and is later displayed when hovering over the field label in a feature form.

Other than the fields contained in the dataset, virtual fields and Auxiliary Storage included, the Source Fields tab also lists fields from any joined layers. Depending on the origin of the field, a different background color is applied to it.

For each listed field, the dialog also lists read-only characteristics such as its type, type name, length and precision. When serving the layer as WMS or WFS, you can also check here which fields could be retrieved.

../../../_images/fields_properties.png

Source Field properties tab

Attributes Form Properties

formView The Attributes Form tab helps you set up the form to display when creating new features or querying existing one. You can define:

  • the look and the behavior of each field in the feature form or the attribute table (label, widget, constraints…);
  • the form’s structure (custom or autogenerated):
  • extra logic in Python to handle interaction with the form or field widgets.

At the top right of the dialog, you can set whether the form is opened by default when creating new features. This can be configured per layer or globally with the Suppress attribute form pop-up after feature creation option in the Settings ‣ Options ‣ Digitizing menu.

Customizing a form for your data

By default, when you click on a feature with the identify Identify Features tool or switch the attribute table to the form view mode, QGIS displays a basic form with predefined widgets (generally spinboxes and textboxes — each field is represented on a dedicated row by its label next to the widget). If relations are set on the layer, fields from the referencing layers are shown in an embedded frame at the bottom of the form, following the same basic structure.

This rendering is the result of the default Autogenerate value of the Attribute editor layout setting in the Layer properties ‣ Attributes Form tab. This property holds three different values:

  • Autogenerate: keeps the basic structure of “one row - one field” for the form but allows to customize each corresponding widget.
  • Drag-and-drop designer: other than widget customization, the form structure can be made more complex eg, with widgets embedded in groups and tabs.
  • Provide ui file: allows to use a Qt designer file, hence a potentially more complex and fully featured template, as feature form.

The autogenerated form

When the Autogenerate option is on, the Available widgets panel shows lists of fields (from the layer and its relations) that would be shown in the form. Select a field and you can configure its appearance and behavior in the right panel:

The drag and drop designer

Choose Drag and drop designer from the Attribute editor layout combobox and you enable a Form Layout panel next to the Available widgets one. From this panel you can create an editor form with several tabs and named groups to present the attribute fields, as shown for example in figure_fields_form.

../../../_images/resulting_feature_form.png

Resulting built-in form with tabs and named groups

To create the form, you can drag and drop fields from the Available Widgets panel to the Form Layout one to have fields added to your custom form and drag and drop fiels inside the Form Layout to reorder their position.

You can also use categories (tab or group frames) to better structure the form. The first step is to use the signPlus icon to create a tab in which fields and groups will be displayed (see figure_fields_layout). You can create as many categories as you want. Use signMinus button to remove any unwanted elements. The next step will be to assign to each category the relevant fields, by simple drag and drop. You can use the same fields many times.

../../../_images/attribute_editor_layout.png

Dialog to create categories with the Attribute editor layout

You can configure tabs or groups with a double-click. QGIS opens a form in which you can:

  • choose to hide or show the item label;
  • rename the category;
  • set over how many columns the fields under the category should be distributed;
  • enter an expression to control the category visibility. The expression will be re-evaluated everytime values in the form change and the tab or groupbox shown/hidden accordingly;
  • show the category as a group box (only available for tabs).

With a double-click on a field label, you can also specify whether the label of its widget should be visible or not in the form.

In case the layer is involved in one or many to many relations (see Creating one or many to many relations), referencing layers are listed in the Relations frame and their form can be embedded in the current layer form by drag-and-drop. Like the other items, double-click the relation label to configure some options:

  • choose to hide or show the item label;
  • show the link button;
  • show the unlink button.

Using custom ui-file

The Provide ui-file option allows you to use complex dialogs made with Qt-Designer. Using a UI-file allows a great deal of freedom in creating a dialog. Note that, in order to link the graphical objects (textbox, combobox…) to the layer’s fields, you need to give them the same name.

Use the Edit UI to define the path to the file to use.

You’ll find some example in the Creating a new form lesson of the QGIS Training Manual. For more advanced information, see https://nathanw.net/2011/09/05/qgis-tips-custom-feature-forms-with-python-logic/.

Enhance your form with custom functions

QGIS forms can have a Python function that is called when the dialog is opened. Use this function to add extra logic to your dialogs. The form code can be specified in three different ways:

  • load from the environment: use a function, for example in startup.py or from an installed plugin)
  • load from an external file: a file chooser will appear in that case to allow you to select a Python file from your filesystem
  • provide code in this dialog: a Python editor will appear where you can directly type the function to use.

In all cases you must enter the name of the function that will be called (open in the example below).

An example is (in module MyForms.py):

def open(dialog,layer,feature):
    geom = feature.geometry()
    control = dialog.findChild(QWidged,"My line edit")

Reference in Python Init Function like so: open

Configure the field behavior

The main part of the Attributes Form tab helps you set the type of widget used to fill or display values of the field, in the attribute table or the feature form: you can define how user interacts with each field and the values or range of values that are allowed to be added to each.

../../../_images/editwidgetsdialog.png

Dialog to select an edit widget for an attribute column

Common settings

Regardless the type of widget applied to the field, there are some common properties you can set to control whether and how a field can be edited.

General options
  • Alias: a human readable name to use for fields. The alias will be displayed in the feature form, the attribute table, or in the Identify results panel. It can also be used as field name replacement in the expression builder, easing expressions understanding and reviews. Aliases are saved in project file.
  • Comment: displays the field’s comment as shown in the Source Fields tab, in a read-only state. This information is shown as tooltip when hovering over the field label in a feature form.
  • checkbox Editable: uncheck this option to set the field read-only (not manually modifiable) even when the layer is in edit mode. Note that checking this setting doesn’t override any edit limitation from the provider.
  • checkbox Label on top: places the field name above or beside the widget in the feature form.
Default values
  • Default value: for new features, automatically populates by default the field with a predefined value or an expression-based one. For example, you can:

    • use $x, $length, $area to automatically populate a field with the feature’s x coordinate, length, area or any geometric information at its creation;
    • increment a field by 1 for each new feature using maximum("field")+1;
    • save the feature creation datetime using now();
    • use variables in expressions, making it easier to e.g. insert the operator name (@user_full_name), the project file path (@project_path), …

    A preview of the resulting default value is displayed at the bottom of the widget.

    Note

    The Default value option is not aware of the values in any other field of the feature being created so it won’t be possible to use an expression combining any of those values i.e using an expression like concat(field1, field2) may not work.

  • checkbox Apply default value on update: whenever the feature attribute or geometry is changed, the default value is recalculated. This could be handy to save values like last user that modifies data, last time it was changed…

Constraints

You can constrain the value to insert in the field. This constraint can be:

  • checkbox Not null: requires the user to provide a value;
  • checkbox Unique: guarantee the inserted value to be unique throughout the field;
  • based on a custom expression: e.g. regexp_match(col0,'A-Za-z') to ensure that the value of the field col0 has only alphabetical letter. A short description can be added to help you remember the constraint.

Whenever a value is added or edited in a field, it’s submitted to the existing constraints and:

  • if it meets all the requirements, a green check is shown beside the field in the form;
  • if it does not meet all the requirements, then a yellow or red cross is displayed near the field. You can hover over the cross to remind which constraints are applied to the field and fix the value:
    • A yellow cross appears when the unmet constraint is an unenforced one and it does not prevent you to save the changes with the “wrong” values;
    • A red cross can not be ignored and does not allow you to save your modifications until they meet the constraints. It appears when the checkbox Enforce constraint option is checked.

Edit widgets

Based on the field type, QGIS automatically determines and assigns a default widget type to it. You can then replace the widget with any other compatible with the field type. The available widgets are:

  • Checkbox: Displays a checkbox whose state defines the value to insert.
  • Classification: Only available when a categorized symbology is applied to the layer, displays a combo box with the values of the classes.
  • Color: Displays a color widget allowing to select a color; the color value is stored as a html notation in the attribute table.
  • Date/Time: Displays a line field which can open a calendar widget to enter a date, a time or both. Column type must be text. You can select a custom format, pop-up a calendar, etc.
  • Enumeration: Opens a combo box with predefined values fetched from the database. This is currently only supported by the PostgreSQL provider, for fields of enum type.
  • Attachment: Uses a “Open file” dialog to store file path in a relative or absolute mode. It can also be used to display a hyperlink (to document path), a picture or a web page.
  • Hidden: A hidden attribute column is invisible. The user is not able to see its contents.
  • Key/Value: Displays a two-columns table to store sets of key/value pairs within a single field. This is currently supported by the PostgreSQL provider, for fields of hstore type.
  • List: Displays a single column table to add different values within a single field. This is currently supported by the PostgreSQL provider, for fields of array type.
  • Range: Allows you to set numeric values from a specific range. The edit widget can be either a slider or a spin box.
  • Relation Reference: This widget lets you embed the feature form of the referenced layer on the feature form of the actual layer. See Creating one or many to many relations.
  • Text Edit (default): This opens a text edit field that allows simple text or multiple lines to be used. If you choose multiple lines you can also choose html content.
  • Unique Values: You can select one of the values already used in the attribute table. If ‘Editable’ is activated, a line edit is shown with autocompletion support, otherwise a combo box is used.
  • Uuid Generator: Generates a read-only UUID (Universally Unique Identifiers) field, if empty.
  • Value Map: A combo box with predefined items. The value is stored in the attribute, the description is shown in the combo box. You can define values manually or load them from a layer or a CSV file.
  • Value Relation: Offers values from a related table in a combobox. You can select layer, key column and value column. Several options are available to change the standard behaviors: allow null value, order by value, allow multiple selections and use of auto-completer. The forms will display either a drop-down list or a line edit field when completer checkbox is enabled.

Tip

Relative Path in Attachment widget

If the path which is selected with the file browser is located in the same directory as the .qgs project file or below, paths are converted to relative paths. This increases portability of a .qgs project with multimedia information attached.

Joins Properties

join The Joins tab allows you to join a loaded attribute table to a loaded vector layer. After clicking signPlus, the Add vector join dialog appears. As key columns, you have to define a join layer you want to connect with the target vector layer. Then, you have to specify the join field that is common to both the join layer and the target layer. Now you can also specify a subset of fields from the joined layer based on the checkbox checkbox Choose which fields are joined. As a result of the join, all information from the join layer and the target layer are displayed in the attribute table of the target layer as joined information. If you specified a subset of fields only these fields are displayed in the attribute table of the target layer.

If the target layer is editable, then some icons will be displayed in the attribute table next to fields, in order to inform their status:

  • joinNotEditable: the join layer is not configured to be editable. If you want to be able to edit join features from the target attribute table, then you have to check the option checkbox Editable join layer.
  • joinedLayerNotEditable: the join layer is well configured to be editable, but its current status is read only.
  • joinHasNotUpsertOnEdit: the join layer is editable but synchronization mechanisms are not activated. If you want to automatically add a feature in the join layer when a feature is created in the target layer, then you have to check the option checkbox Upsert on edit. Symmetrically, the option checkbox Delete cascade may be activated if you want to automatically delete join features.

Moreover, the checkbox Dynamic form option helps to synchronize join fields on the fly, according to the Target field. This way, constraints for join fields are also correctly updated. Note that it’s deactivated by default because it may be very time consuming if you have a lot of features or a myriad of joins.

Otherwise, the checkbox Cache join layer in virtual memory option allows to cache values in memory (without geometries) from the joined layer in order to speed up lookups.

QGIS currently has support for joining non-spatial table formats supported by OGR (e.g., CSV, DBF and Excel), delimited text and the PostgreSQL provider (see figure_joins).

../../../_images/join_attributes.png

Join an attribute table to an existing vector layer

Additionally, the add vector join dialog allows you to:

  • checkbox Create attribute index on the join field
  • checkbox Choose which fields are joined
  • Create a checkbox Custom field name prefix

Auxiliary Storage Properties

The regular way to customize styling and labeling is to use data-defined properties as described in Data defined override setup. However, it may not be possible if the underlying data is read only. Moreover, configuring these data-defined properties may be very time consuming or not desirable! For example, if you want to fully use map tools coming with The Label Toolbar, then you need to add and configure more than 20 fields in your original data source (x and y positions, rotation angle, font style, color and so on).

The Auxiliary Storage mechanism provides the solution to these limitations and awkward configurations. Actually, auxiliary fields are a roundabout mean to automatically manage and store these data-defined properties (labels, diagram, symbology…) in a SQLite database thanks to editable joins. This way, data source doesn’t even need to be editable!

A tab is available in vector layer properties dialog to manage auxiliary storage:

../../../_images/auxiliary_storage_tab.png

Auxiliary Storage tab

Labeling

Considering that the data source may be customized thanks to data-defined properties without being editable, labeling map tools described in The Label Toolbar are always available as soon as labeling is activated.

Actually, the auxiliary storage system needs an auxiliary layer to store these properties in a SQLite database (see Auxiliary storage database). Its creation process is run the first time you click on the map while a labeling map tool is currently activated. Then, a window is displayed, allowing to indicate the primary key to use for joining (to ensure that features are uniquely identified):

../../../_images/auxiliary_storage_key.png

Auxiliary Layer creation dialog

As soon as an auxiliary layer is configured for the current data source, you can retrieve its information in the tab:

../../../_images/auxiliary_storage_tabkey.png

Auxiliary Layer key

For now, we can see that:

  • the primary key used is well id
  • there’s 0 feature using an auxiliary field
  • there’s 0 auxiliary field

Now that the auxiliary layer is well created, we just have to edit our labels. If we click on a label while the changeLabelProperties Change Label map tool is activated, then we’re able to update styling properties like sizes, colors and so on. Then, the corresponding data-defined properties are created and can be retrieved:

../../../_images/auxiliary_storage_fields.png

Auxiliary Fields

As we are seeing in the previous figure, 21 fields have been automatically created and configured for labeling. For example, the Color auxiliary field type is a String and is named labeling_color in the underlying SQLite database. Moreover, we observe that there’s 1 entity which is currently using these auxiliary fields (according to the current example).

By the way, considering that auxiliary fields are linked to data-defined properties, we can observe that data-defined override options are setup correctly because of the icon dataDefineOn in the labeling tab:

../../../_images/auxiliary_storage_dd.png

Data-defined properties automatically created

Otherwise, there’s another way to create an auxiliary field for a specific property thanks to the dataDefined data-defined override button. By clicking on Store data in the project, an auxiliary field is automatically created for the Opacity field. If you click on this button whereas the auxiliary layer is not created yet, then the window Auxiliary Layer creation dialog is firstly displayed to select the primary key to use for joining.

Symbology

In the same way than for customizing labels, auxiliary fields may be used to stylize symbols too. To do this, you just have to click on Store data in the project for a specific symbol property. For example for the Fill color field:

../../../_images/auxiliary_storage_symbol.png

Data-defined property menu for symbol

Because you may customize same property for different (levels of) symbols, each setting requires a unique name to avoid conflict. Thus, by clicking on Store data in the project, a window is displayed, indicating the Type of the field and providing a way to give the unique name. For the Fill color field, the next window is opened:

../../../_images/auxiliary_storage_symbol_name.png

Name of the auxiliary field for a symbol

Once created, the auxiliary field can be retrieved in the auxiliary storage tab:

../../../_images/auxiliary_storage_symbol_field.png

Auxiliary field symbol

Attribute table and widgets

Once created, auxiliary fields may be edited through the attribute table. However, there’s some subtlety about widgets of auxiliary fields.

For example, auxiliary fields which may be edited through an external tool are not visible in the attribute table. This way, as the Rotation may be edited through changeLabelProperties Change Label or rotateLabel Rotate Label, the auxiliary widget is Hidden by default (see Edit widgets). However, as the Opacity field cannot be edited thanks to map tools, the corresponding widget is not Hidden. Moreover, auxiliary fields representing a Color have a widget Color set by default.

Then, the underlying form will look like the next figure:

../../../_images/auxiliary_storage_widgets.png

Form with auxiliary fields

Management

Some actions are available to manage auxiliary layers thanks to the next combobox:

../../../_images/auxiliary_storage_actions.png

Auxiliary layer management

The first item Create is disabled in this case because the auxiliary layer is already created. But in case of a fresh work, you can use this action to create an auxiliary layer. As explained in Labeling, a primary key will be needed then.

The Clear action allows to keep all auxiliary fields, but remove their contents. This way, the number of features using these fields will fall to 0.

The Delete action completely removes the auxiliary layer. In other words, the corresponding table is deleted from the underlying SQLite database and properties customization are lost.

Finally, the Export action allows to save the auxiliary layer as a new vector layer. Note that geometries are not stored in auxiliary storage. However, in this case, geometries are exported from the original data source too.

Auxiliary storage database

When you save your project with the .qgs format, the SQLite database used for auxiliary storage is saved at the same place but with the extension .qgd.

For convenience, an archive may be used instead thanks to the .qgz format. In this case, .qgd and .qgs files are both embedded in the archive.

Actions Properties

action QGIS provides the ability to perform an action based on the attributes of a feature. This can be used to perform any number of actions, for example, running a program with arguments built from the attributes of a feature or passing parameters to a web reporting tool.

../../../_images/action_dialog.png

Overview action dialog with some sample actions

Actions are useful when you frequently want to run an external application or view a web page based on one or more values in your vector layer. They are divided into six types and can be used like this:

  • Generic, Mac, Windows and Unix actions start an external process.
  • Python actions execute a Python expression.
  • Generic and Python actions are visible everywhere.
  • Mac, Windows and Unix actions are visible only on the respective platform (i.e., you can define three ‘Edit’ actions to open an editor and the users can only see and execute the one ‘Edit’ action for their platform to run the editor).

There are several examples included in the dialog. You can load them by clicking on Create Default Actions. To edit any of the examples, double-click its row. One example is performing a search based on an attribute value. This concept is used in the following discussion.

The checkbox Show in Attribute Table allows you to display in the attribute table dialog the checked feature-scoped actions, either as Combo Box or as Separate Buttons (see Configuring the columns).

Defining Actions

To define an attribute action, open the vector Layer Properties dialog and click on the Actions tab. In the Actions tab, click the signPlus Add a new action to open the Edit Action dialog.

Select the action Type and provide a descriptive name for the action. The action itself must contain the name of the application that will be executed when the action is invoked. You can add one or more attribute field values as arguments to the application. When the action is invoked, any set of characters that start with a % followed by the name of a field will be replaced by the value of that field. The special characters %% will be replaced by the value of the field that was selected from the identify results or attribute table (see using_actions below). Double quote marks can be used to group text into a single argument to the program, script or command. Double quotes will be ignored if preceded by a backslash.

The Action Scopes allows you to define where the action should be available. You have 4 different choices:

  1. Feature Scope: action is available when right click in the cell within the attribute table.
  2. Field Scope: action is available when right click in the cell within the attribute table, in the feature form and in the default action button of the main toolbar.
  3. Layer Scope: action is available in the action button in the attribute table toolbar. Be aware that this type of action involves the entire layer and not the single features.
  4. Canvas: action is available in the main action button in the toolbar.

If you have field names that are substrings of other field names (e.g., col1 and col10), you should indicate that by surrounding the field name (and the % character) with square brackets (e.g., [%col10]). This will prevent the %col10 field name from being mistaken for the %col1 field name with a 0 on the end. The brackets will be removed by QGIS when it substitutes in the value of the field. If you want the substituted field to be surrounded by square brackets, use a second set like this: [[%col10]].

Using the Identify Features tool, you can open the Identify Results dialog. It includes a (Derived) item that contains information relevant to the layer type. The values in this item can be accessed in a similar way to the other fields by proceeding the derived field name with (Derived).. For example, a point layer has an X and Y field, and the values of these fields can be used in the action with %(Derived).X and %(Derived).Y. The derived attributes are only available from the Identify Results dialog box, not the Attribute Table dialog box.

Two example actions are shown below:

  • konqueror https://www.google.com/search?q=%nam
  • konqueror https://www.google.com/search?q=%%

In the first example, the web browser konqueror is invoked and passed a URL to open. The URL performs a Google search on the value of the nam field from our vector layer. Note that the application or script called by the action must be in the path, or you must provide the full path. To be certain, we could rewrite the first example as: /opt/kde3/bin/konqueror https://www.google.com/search?q=%nam. This will ensure that the konqueror application will be executed when the action is invoked.

The second example uses the %% notation, which does not rely on a particular field for its value. When the action is invoked, the %% will be replaced by the value of the selected field in the identify results or attribute table.

Using Actions

QGIS offers many ways to execute actions you enabled on a layer. Depending on their settings, they can be available:

  • in the drop-down menu of actionRun Run Feature Action button from the Attributes toolbar or Attribute table dialog;
  • when right-clicking a feature with the identify Identify Features tool (see Identifying Features for more information);
  • from the Identify Results panel, under the Actions section;
  • as items of an Actions column in the Attribute Table dialog.

If you are invoking an action that uses the %% notation, right-click on the field value in the Identify Results dialog or the Attribute Table dialog that you wish to pass to the application or script.

Here is another example that pulls data out of a vector layer and inserts it into a file using bash and the echo command (so it will only work on nix or perhaps osx). The layer in question has fields for a species name taxon_name, latitude lat and longitude long. We would like to be able to make a spatial selection of localities and export these field values to a text file for the selected record (shown in yellow in the QGIS map area). Here is the action to achieve this:

bash -c "echo \"%taxon_name %lat %long\" >> /tmp/species_localities.txt"

After selecting a few localities and running the action on each one, opening the output file will show something like this:

Acacia mearnsii -34.0800000000 150.0800000000
Acacia mearnsii -34.9000000000 150.1200000000
Acacia mearnsii -35.2200000000 149.9300000000
Acacia mearnsii -32.2700000000 150.4100000000

As an exercise, we can create an action that does a Google search on the lakes layer. First, we need to determine the URL required to perform a search on a keyword. This is easily done by just going to Google and doing a simple search, then grabbing the URL from the address bar in your browser. From this little effort, we see that the format is https://www.google.com//search?q=QGIS, where QGIS is the search term. Armed with this information, we can proceed:

  1. Make sure the lakes layer is loaded.

  2. Open the Layer Properties dialog by double-clicking on the layer in the legend, or right-click and choose Properties from the pop-up menu.

  3. Click on the Actions tab.

  4. Click signPlus Add a new action.

  5. Choose the Open action type,

  6. Enter a name for the action, for example Google Search.

  7. Additionally you can add a Short Name or even an Icon.

  8. Choose the action Scope. See Defining Actions for further information. Leave the default settings for this example.

  9. For the action, we need to provide the name of the external program to run. In this case, we can use Firefox. If the program is not in your path, you need to provide the full path.

  10. Following the name of the external application, add the URL used for doing a Google search, up to but not including the search term: https://www.google.com//search?q=

  11. The text in the Action field should now look like this: https://www.google.com//search?q=

  12. Click on the drop-down box containing the field names for the lakes layer. It’s located just to the left of the Insert button.

  13. From the drop-down box, select ‘NAMES’ and click Insert.

  14. Your action text now looks like this:

    https://www.google.com//search?q=[%NAMES%]

  15. To finalize and add the action, click the OK button.

../../../_images/add_action_edit.png

Edit action dialog configured with the example

This completes the action, and it is ready to use. The final text of the action should look like this:

https://www.google.com//search?q=[%NAMES%]

We can now use the action. Close the Layer Properties dialog and zoom in to an area of interest. Make sure the lakes layer is active and identify a lake. In the result box you’ll now see that our action is visible:

../../../_images/action_identifyaction.png

Select feature and choose action

When we click on the action, it brings up Firefox and navigates to the URL https://www.google.com/search?q=Tustumena. It is also possible to add further attribute fields to the action. Therefore, you can add a + to the end of the action text, select another field and click on Insert Field. In this example, there is just no other field available that would make sense to search for.

You can define multiple actions for a layer, and each will show up in the Identify Results dialog.

You can also invoke actions from the attribute table by selecting a row and right-clicking, then choosing the action from the pop-up menu.

There are all kinds of uses for actions. For example, if you have a point layer containing locations of images or photos along with a file name, you could create an action to launch a viewer to display the image. You could also use actions to launch web-based reports for an attribute field or combination of fields, specifying them in the same way we did in our Google search example.

We can also make more complex examples, for instance, using Python actions.

Usually, when we create an action to open a file with an external application, we can use absolute paths, or eventually relative paths. In the second case, the path is relative to the location of the external program executable file. But what about if we need to use relative paths, relative to the selected layer (a file-based one, like Shapefile or SpatiaLite)? The following code will do the trick:

command = "firefox"
imagerelpath = "images_test/test_image.jpg"
layer = qgis.utils.iface.activeLayer()
import os.path
layerpath = layer.source() if layer.providerType() == 'ogr'
  else (qgis.core.QgsDataSourceURI(layer.source()).database()
    if layer.providerType() == 'spatialite' else None)
path = os.path.dirname(str(layerpath))
image = os.path.join(path,imagerelpath)
import subprocess
subprocess.Popen( [command, image ] )

We just have to remember that the action is one of type Python and the command and imagerelpath variables must be changed to fit our needs.

But what about if the relative path needs to be relative to the (saved) project file? The code of the Python action would be:

command = "firefox"
imagerelpath = "images/test_image.jpg"
projectpath = qgis.core.QgsProject.instance().fileName()
import os.path
path = os.path.dirname(str(projectpath)) if projectpath != '' else None
image = os.path.join(path, imagerelpath)
import subprocess
subprocess.Popen( [command, image ] )

Another Python action example is the one that allows us to add new layers to the project. For instance, the following examples will add to the project respectively a vector and a raster. The names of the files to be added to the project and the names to be given to the layers are data driven (filename and layername are column names of the table of attributes of the vector where the action was created):

qgis.utils.iface.addVectorLayer('/yourpath/[% "filename" %].shp',
  '[% "layername" %]', 'ogr')

To add a raster (a TIF image in this example), it becomes:

qgis.utils.iface.addRasterLayer('/yourpath/[% "filename" %].tif',
  '[% "layername" %]')

Display Properties

display The Display tab helps you configure fields to use for feature identification:

  • The Display name: based on a field or an expression. This is:
    • the label shown on top of the feature information in the Identify tool results;
    • the field used in the locator bar when looking for features in all layers;
    • the feature identifier in the attribute table form view;
    • the map tip information, i.e. the message displayed in the map canvas when hovering over a feature of the active layer with the mapTips Show Map Tips icon pressed. Applicable when no HTML Map Tip is set.
  • The HTML Map Tip is specifically created for the map tips: it’s a more complex and full HTML text mixing fields, expressions and html tags (multiline, fonts, images, hyperlink…).
../../../_images/display_html.png

HTML code for map tip

To activate map tips, select the menu option View ‣ Show Map Tips or click on the mapTips Show Map Tips icon of the Attributes Toolbar. Map tip is a cross-session feature meaning that once activated, it stays on and apply to any layer in any project, even in future QGIS sessions until it’s toggled off.

../../../_images/map_tip.png

Map tip made with HTML code

Rendering Properties

Scale dependent visibility

You can set the Maximum (inclusive) and Minimum (exclusive) scale, defining a range of scale in which features will be visible. Out of this range, they are hidden. The mapIdentification Set to current canvas scale button helps you use the current map canvas scale as boundary of the range visibility. See Scale Dependent Rendering for more information.

Simplify geometry

QGIS offers support for on-the-fly feature generalisation. This can improve rendering times when drawing many complex features at small scales. This feature can be enabled or disabled in the layer settings using the checkbox Simplify geometry option. There is also a global setting that enables generalisation by default for newly added layers (see global simplification for more information).

../../../_images/simplify_rendering.png

Layer Geometry Simplification dialog

Note

Feature generalisation may introduce artefacts into your rendered output in some cases. These may include slivers between polygons and inaccurate rendering when using offset-based symbol layers.

While rendering extremely detailed layers (e.g. polygon layers with a huge number of nodes), this can cause layout exports in PDF/SVG format to be huge as all nodes are included in the exported file. This can also make the resultant file very slow to work with/open in other programs.

Checking checkbox Force layer to render as raster forces these layers to be rasterised so that the exported files won’t have to include all the nodes contained in these layers and the rendering is therefore sped up.

You can also do this by forcing the layout to export as a raster, but that is an all-or-nothing solution, given that the rasterisation is applied to all layers.

Refresh layer at interval (seconds): set a timer to automatically refresh individual layers at a matching interval. Canvas updates are deferred in order to avoid refreshing multiple times if more than one layer has an auto update interval set.

Depending on the data provider (e.g. PostgreSQL), notifications can be sent to QGIS when changes are applied to the data source, out of QGIS. Use the checkbox Refresh layer on notification option to trigger an update. You can also limit the layer refresh to a specific message set in the checkbox Only if message is text box.

Variables Properties

expression The Variables tab lists all the variables available at the layer’s level (which includes all global and project’s variables).

It also allows the user to manage layer-level variables. Click the signPlus button to add a new custom layer-level variable. Likewise, select a custom layer-level variable from the list and click the signMinus button to remove it.

More information on variables usage in the General Tools Storing values in Variables section.

Metadata Properties

editMetadata The Metadata tab provides you with options to create and edit a metadata report on your layer. Information to fill concern:

  • the data Identification: basic attribution of the dataset (parent, identifier, title, abstract, language…);
  • the Categories the data belongs to. Alongside the ISO categories, you can add custom ones;
  • the Keywords to retrieve the data and associated concepts following a standard based vocabulary;
  • the Access to the dataset (licenses, rights, fees, and constraints);
  • the Extent of the dataset, either spatial one (CRS, map extent, altitudes) or temporal;
  • the Contact of the owner(s) of the dataset;
  • the Links to ancillary resources and related information;
  • the History of the dataset.

A summary of the filled information is provided in the Validation tab and helps you identify potential issues related to the form. You can then either fix them or ignore them.

Metadata are currently saved in the project file. It can also be saved as an .XML file alongside file based layers or in a local .sqlite database for remote layers (e.g. PostGIS).

Dependencies Properties

dependencies The Dependencies tab allows to declare data dependencies between layers. A data dependency occurs when a data modification in a layer, not by direct user manipulation, may modify data of other layers. This is the case for instance when geometry of a layer is updated by a database trigger or custom PyQGIS scripting after modification of another layer’s geometry.

In the Dependencies tab, you can select any layers which may externally alter the data in the current layer. Correctly specifying dependent layers allows QGIS to invalidate caches for this layer when the dependent layers are altered.

Legend Properties

legend The Legend properties tab provides you with advanced settings for the Layers panel and/or the print layout legend. These options include:

  • checkbox Text on symbols: In some cases it can be useful to add extra information to the symbols in the legend. With this frame, you can affect to any of the symbols used in the layer symbology a text that is displayed over the symbol, in both Layers panel and print layout legend. This mapping is done by typing each text next to the symbol in the table widget or filling the table using the Set Labels from Expression button. Text appearance is handled through the font and color selector widgets of the Text Format button.
../../../_images/text_legend_symbols.png

Setting text on symbols (left) and its rendering in Layers panel (right)

  • a list of widgets you can embed within the layer tree in the Layers panel. The idea is to have a way to quickly access some actions that are often used with the layer (setup transparency, filtering, selection, style or other stuff…).

    By default, QGIS provides transparency widget but this can be extended by plugins registering their own widgets and assign custom actions to layers they manage.

QGIS Server Properties

overlay The QGIS Server tab consists of Description, Attribution, MetadataURL, LegendUrl and Properties sections.

In the Properties section, you get general information about the layer, including specifics about the type and location, number of features, feature type, and editing capabilities. The Extents table provides you with information on the layer extent and the Layer Spatial Reference System, which is information about the CRS of the layer. This can provide a quick way to get useful information about the layer.

Additionally, you can add or edit a title and abstract for the layer in the Description section. It’s also possible to define a Keyword list here. These keyword lists can be used in a metadata catalog. If you want to use a title from an XML metadata file, you have to fill in a link in the DataUrl field.

Use Attribution to get attribute data from an XML metadata catalog.

In MetadataUrl, you can define the general path to the XML metadata catalog. This information will be saved in the QGIS project file for subsequent sessions and will be used for QGIS server.

In the LegendUrl section, you can provide the url of a legend image in the url field. You can use the Format drop-down option to apply the appropriate format of the image. Currently png, jpg and jpeg image formats are supported.

../../../_images/vector_metadata_tab.png

QGIS Server tab in vector layers properties dialog