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, double-click on a layer in the legend or right-click on the layer and select Properties from the pop-up menu.
Tip
Switch quickly between different layer representations
Using the Styles ‣ Add combobox at the bottom of the Layer Properties dialog, you can save as many combinations of layer properties settings (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.
Use this menu to make general settings for the vector layer.
There are several options available:
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 Set to current canvas scale button helps
you use the current map canvas scale as boundary of the range visibility.
Figure Vector General 1:
General menu in vector layers properties dialog
Under the Provider Feature Filter frame, the Query Builder 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. The query result can be saved as a new vector layer.
The Query Builder is accessible through the eponym term at the bottom of the General menu in the Layer Properties. Under Feature subset, click on the [Query Builder] button to open the Query builder. For example, if you have a regions layer with a TYPE_2 field, you could select only regions that are borough in the Provider specific filter expression box of the Query Builder. Figure_vector_general_2 shows an example of the Query Builder populated with the regions.shp layer from the QGIS sample data. The Fields, Values and Operators sections help you to construct the SQL-like query.
Figure Vector General 2:
Query Builder
The Fields list contains all attribute columns of the attribute table to be searched. To add an attribute column to the SQL WHERE clause field, double click its name in the Fields list. Generally, you can use the various fields, values and operators to construct the query, or you can just type it into the SQL box.
The Values list lists the values of an attribute table. To list all possible values of an attribute, select the attribute in the Fields list and click the [all] button. To list the first 25 unique values of an attribute column, select the attribute column in the Fields list and click the [Sample] button. To add a value to the SQL WHERE clause field, double click its name in the Values 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 shows a message box with the number of features satisfying the current query, which is useful in the process of query construction. The [Clear] button clears the text in the SQL WHERE clause text field. The [OK] button closes the window and selects the features satisfying the query. The [Cancel] button closes the window without changing the current selection.
QGIS treats the resulting subset acts as if it where the entire layer. For example if you applied the filter above for ‘Borough’, you can not display, query, save or edit Anchorage, because that is a ‘Municipality’ and therefore not part of the subset.
The only exception is that unless your layer is part of a database, using a subset will prevent you from editing the layer.
The Style menu 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
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.
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 renderer.
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.
Catatan
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.
The 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.
Figure Symbology 1:
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 style 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 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.
The Categorized Renderer is used to render
all features from a layer, using an user-defined symbol whose aspect reflects
the value of a selected feature’s attribute. The Categorized menu allows
you to select:
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_symbology_2 shows the category rendering dialog used for the rivers layer of the QGIS sample dataset.
Figure Symbology 2:
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.
The 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:
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.
Catatan
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:
The listbox in the center part of the Style menu 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_symbology_3 shows the graduated rendering dialog for the rivers layer of the QGIS sample dataset.
Figure Symbology 3:
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
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 are not rendering types available from the Style rendering drop-down list. However with the Size Assistant 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
Proportional rendering is done by first applying to the layer the Single Symbol Renderer.
Once you set the symbol, at the upper level of the symbol tree, the
Data-defined override button available beside
Size or Width options (for point or line layers
respectively) provides tool to create proportional symbology for the layer.
An assistant is moreover accessible through the
menu
to help you define size expression.
Figure Symbology 4:
Varying size assistant
The assistant lets you define:
To the right side of the dialog, you can preview the features representation within a live-update widget. This representation is added to the layer tree in the layer legend and is also used to shape the layer representation in the print composer legend item.
The values presented in the varying size assistant above will set the size ‘Data-defined override’ with:
coalesce(scale_exp(Importance, 1, 20, 2, 10, 0.57), 1)
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 first apply a categorized or graduated rendering on a layer, using the same type of symbol for all the classes. Then, clicking on the symbol [Change] button above the classification frame, you get the The symbol Selector dialog from which, as seen above, you can activate and set the size assistant option either on size (for point layer) or width (for line layer).
Like the proportional symbol, the size-related symbol is added to the layer tree, at the top of the categorized or graduated classes symbols. And both representation are also available in the print composer legend item.
The 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.
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, activate an existing row by double-clicking on it, or
click on ‘+’ and click on the new rule. In the Rule properties dialog,
you can define a label for the rule. Press the button to open the
expression string builder.
In the Function List, click on Fields and Values to view all
attributes of the attribute table to be searched.
To add an attribute to the field calculator Expression field,
double click on its name in the Fields and Values list. Generally, you
can use the various fields, values and functions to construct the calculation
expression, or you can just type it into the box (see Expressions).
You can create a new rule by copying and pasting an existing rule with the right
mouse button. You can also use the ‘ELSE’ rule that will be run if none of the other
rules on that level matches.
Since QGIS 2.8 the rules appear in a tree hierarchy in the map legend. Just
double-click the rules in the map legend and the Style menu of the layer properties
appears showing the rule that is the background for the symbol in the tree.
The example in figure_symbology_5 shows the rule-based rendering dialog for the rivers layer of the QGIS sample dataset.
Figure Symbology 5:
Rule-based Symbolizing options
The Point Displacement renderer
works to visualize all features of a point layer, even if they have the same location.
To do this, the symbols of the points are placed on a displacement circle
around one center symbol or on several concentric circles.
Figure Symbology 6:
Point displacement dialog
Catatan
You can still render features with other renderer like Single symbol, Graduated, Categorized or Rule-Based renderer using the Renderer drop-down list then the Renderer Settings... button.
The 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 2.5 D renderer.
Figure Symbology 7:
Inverted Polygon dialog
With the 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.
Figure Symbology 8:
Heatmap dialog
Using the 2.5 D renderer it’s possible to create
a 2.5 D 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
Shade walls based on aspect option. You can also
simulate a shadow by setting a Color and Size (in map
units).
Figure Symbology 9:
2.5 D dialog
Tip
Using 2.5 D effect with other renderers
Once you have finished setting the basic style on the 2.5 D renderer, you can convert this to another renderer (single, categorized, graduated). The 2.5 D 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 2.5 D representation or add some extra styling to your 2.5 D 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 2.5 D 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.
From the Style tab, you can also set some options that invariabily act on all features of the layer:
Layer transparency : 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.
Layer blending mode and Feature blending mode: 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 button beside.
You then get the Define Order dialog in which you:
You can add several rules of ordering. The first rule is applied to all the features in the layer, z-ordering them according to the value returned. Then, for each group of features with the same value (including those with NULL value) and thus same z-level, the next rule is applied to sort its items among them. And so on...
Once the Define Order dialog is applied, a summary of the expression(s)
used to control the layer rendering is retranscribed in the textbox
beside Control feature rendering order option.
Figure Layer Rendering 1:
Layer rendering options
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 rendering the option is directly available through [Symbols levels] button, while for Point displacement renderer the same button is inside the Rendering settings dialog.
To activate symbols levels, select the 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.
Figure Symbols levels 1:
Symbol levels dialog
Catatan
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.
Figure Symbols levels 2:
Symbol levels activated (A) and deactivated (B) difference
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 Draw Effects options,
which adds paint effects for customizing the visualization of vector layers.
The option is available in the Layer Properties –> Style 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 Draw effects option
and clicking the
Customize effects button, that will open
the Effect Properties Dialog (see figure_effects_1). 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.
Figure Effects 1:
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.
Figure Effects 2:
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 Grayscale to select how to create it
(options are: ‘lightness’, ‘luminosity’ and ‘average’). If
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.
Figure Effects 3:
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.
Figure Effects 4:
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.
Figure Effects 5:
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.
Figure Effects 6:
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.
Figure Effects 7:
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:
Figure Effects 8:
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 Effect type option. You can reorder the effects
using
Move up and
Move down
buttons, and also add/remove effects using the
Add effect
and
Remove effect buttons.
There is also a 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).
The Labels core application provides smart
labeling for vector point, line and polygon layers, and only requires a
few parameters. This application also supports on-the-fly transformed layers.
The following menus are used to configure the labeling of vector layers:
To label a layer start QGIS and load a vector layer. Activate the layer
in the legend and click on the Layer Labeling Options
icon in the QGIS toolbar menu or activate the Labels tab in the
layer properties dialog.
The first step is to choose the labeling method from the drop-down list. There are four options available:
Select the Show labels for this layer option and then select an attribute
column to use for labeling from the Label with drop-down list. Click
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 an use-case.
You can define the text style in the Text menu (see Figure_labels_1). Use the Type case option to influence the text rendering. You have the possibility to render the text ‘All uppercase’, ‘All lowercase’ or ‘Capitalize first letter’. Use the Blending Modes to create effects known from graphics programs.
Figure Labels 1:
Smart labeling of vector point layers
In the Formatting menu, you can define a character for a line break in the labels with the ‘Wrap on character’ function. You can format the Line Height and the alignment. For the latter typical values are available plus Follow label placement. 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, and if it is placed to the right of the point then the label will be left aligned.
For line vector layers you can include line directions symbols. There are options specifying the type of symbol and the symbol placement.
Use the Formatted numbers option to format the numbers in
an attribute table. Here, decimal places may be inserted.
If you enable this option, three decimal places are initially set by default.
To create a buffer, just activate the Draw text buffer
checkbox in the Buffer menu.
The buffer color is variable. Here, you can also use blend modes.
If the
color buffer’s fill checkbox is activated, it will
interact with partially transparent text and give mixed color transparency
results. Turning off the buffer fill fixes that issue (except where the interior
aspect of the buffer’s stroke intersects with the text’s fill) and also allows
you to make outlined text.
In the Background menu, 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).
Use the Shadow menu for a user-defined 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 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.
Choose the Placement menu 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.
With the Cartographic placement mode,
point labels are generated with best 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:
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 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.
In the Offset from point placement, 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 X and Y offset 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.
Label options for line layers include Parallel,
Curved or
Horizontal.
For the
Parallel and
Curved options, you can set the position to
Above line,
On line and
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 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
Curved option (see Figure_labels_2 ).
For all three placement options you can set up a minimum distance for repeating labels. The distance can be in mm or in map units.
Figure Labels 2:
Smart labeling of vector line layers
You can choose one of the following options for placing labels in polygons:
Offset from centroid,
Horizontal
(slow),
Around centroid,
Free and
Using perimeter.
In the Offset from centroid settings you can specify
if the centroid is of the
visible polygon or
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
visible polygon
or
whole polygon for the centroid.
With the Using perimeter settings, you can define a
position and a distance for the label. For the position,
Above line,
On line,
Below line and
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.
Figure Labels 3:
Smart labeling of vector polygon layers
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 interact with labels of the 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.
In the Rendering menu, 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:
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 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 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
data-defined override control next to the option.
The 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:
QGIS allows to use expressions to label features. Just click the
icon in the
Labels
menu of the properties dialog. In figure_labels_4 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.
Figure Labels 4:
Expression based labeling is easy to work with. All you have to take care of is that:
Let’s have a look at some examples:
# label based on two fields 'name' and 'place' with a comma as separator
"name" || ', ' || "place"
-> John Smith, Paris
# 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")
-> My name is John Smith and I live in Paris
# 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)
-> My name is John Smith and I live in Paris
-> My name is John Smith # if the field 'place' is NULL
# multi-line label based on two fields 'name' and 'place' with a descriptive text
concat('My name is ', "name", '\n' , 'I live in ' , "place")
-> My name is John Smith
I live in Paris
# label based on a field and the $area function
# to show the place name and its rounded area size in a converted unit.
'The area of ' || "place" || ' has a size of ' || round($area/10000) || ' ha'
-> The area of Paris has a size of 10500 ha
# create a CASE ELSE condition. If the population value in field
# population is <= 50000 it is a town, otherwise a city.
concat('This place is a ', CASE WHEN "population <= 50000" THEN 'town' ELSE 'city' END)
-> This place is a town
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.
With the data-defined override functions, the settings for the labeling
are overridden by entries in the attribute table.
You can activate and deactivate the function with the right-mouse button.
Hover over the symbol and you see the information about the data-defined override,
including the current definition field.
We now describe an example using the data-defined override function for the
Move label function (see figure_labels_5 ).
Figure Labels 5:
Labeling of vector polygon layers with data-defined override
Figure Labels 6:
Move labels
With Rule-based labeling multiple label configurations can be defined and applied selectively on the base of expression filters, as in Rule-based rendering.
Rules can be set selecting the corresponding option at the top of the Labels panel (see figure_labels_7 ).
Figure Labels 7:
Rule based labeling panel
To create a rule, activate an existing row by double-clicking on it, or click on ‘+’ and click on the new rule. Within the panel you can set the filter expression and the related label configurations.
Figure Labels 8:
Rule settings
Within the Fields menu, the field attributes of the
selected dataset can be manipulated. The buttons
New Column and
Delete Column
can be used when the dataset is in
Editing mode.
Edit Widget
Figure Fields 1:
Dialog to select an edit widget for an attribute column
Within the Fields menu, you also find an edit widget column. This column can be used to define values or a range of values that are allowed to be added to the specific attribute table column. If you click on the [edit widget] button, a dialog opens, where you can define different widgets. These widgets are:
Catatan
QGIS has an advanced ‘hidden’ option to define your own field widget using python and add it to this impressive list of widgets. It is tricky but it is very well explained in following excellent blog that explains how to create a real time validation widget that can be used like described widgets. See http://blog.vitu.ch/10142013-1847/write-your-own-qgis-form-elements
Tip
Relative Path in widgets
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. This is enabled only for File Name, Photo and Web View at this moment.
With the Attribute editor layout, you can now define built-in forms (see figure_fields_2). This is useful for data entry jobs or to identify objects using the option auto open form when you have objects with many attributes. You can create an editor with several tabs and named groups to present the attribute fields.
Choose ‘Drag and drop designer’ and an attribute column. Use the
icon to create a category to insert a tab or a named group (see figure_fields_3).
When creating a new category, QGIS will insert a new tab or named group for the
category in the built-in form.
The next step will be to assign the relevant fields to a selected category
with the
icon. You can create more categories and use the
same fields again.
Other options in the dialog are ‘Autogenerate’ and ‘Provide ui-file’.
QGIS dialogs 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:
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
Figure Fields 2:
Dialog to create categories with the Attribute editor layout
Figure Fields 3:
Resulting built-in form with tabs and named groups
The Joins menu allows you to join a loaded attribute
table to a loaded vector layer. After clicking
, 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
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.
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_1).
Figure Joins 1:
Join an attribute table to an existing vector layer
Additionally, the add vector join dialog allows you to:
The Diagrams menu allows you to add a graphic overlay to
a vector layer (see figure_diagrams_1).
The current core implementation of diagrams provides support for:
For each type of diagram, the menu is divided into five tabs:
Attributes defines which variables to display in the diagram.
Use 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 atributes are displayed. You can also change the label in the ‘Legend’ column or the attibute color by double-clicking the item.
This label is the default text displayed in the legend of the print composer or of the layer tree.
Figure Diagrams 1:
Vector properties dialog with diagram menu
Appearance defines how the diagram looks like. It provides general settings that do not interfere with the statistic values such as:
In this menu, you can also manage the diagram visibility:
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 :
Figure Diagrams 2:
Vector properties dialog with diagram menu, Size tab
Placement helps to define diagram position. According to the layer geometry type, it offers different options for the placement:
The diagram can also be placed using feature data by filling the X and Y fields with an attribute of the feature.
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 or the z-index value.
The Options tab has settings only in case of histogram. You can choose whether the bar orientation should be ‘Up’, ‘Down’, ‘Right’ and ‘Left’.
Tip
Switch quickly between diagrams
Given that almost all the settings above are 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.
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 Contoh data).
Figure Diagrams 3:
Remember that in the Position tab, a 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 button to add an expression.
See Expressions chapter for more information and example.
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.
Figure Actions 1:
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:
There are several examples included in the dialog. You can load them by clicking on [Add default actions]. One example is performing a search based on an attribute value. This concept is used in the following discussion.
Attribute actions are defined from the vector Layer Properties dialog. To define an action, open the vector Layer Properties dialog and click on the Actions menu. Go to the Action properties. Select ‘Generic’ as 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.
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:
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 http://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.
Actions can be invoked from either the Identify Results dialog,
an Attribute Table dialog or from Run Feature Action
(recall that these dialogs can be opened by clicking
Identify Features or
Open Attribute Table or
Run Feature Action). To invoke an action, right
click on the record and choose the action from the pop-up menu. Actions are
listed in the popup menu by the name you assigned when defining the action.
Click on the action you wish to invoke.
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
or perhaps
). 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 http://google.com/search?q=qgis, where QGIS is the search term. Armed with this information, we can proceed:
Make sure the lakes layer is loaded.
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.
Click on the Actions menu.
Enter a name for the action, for example Google Search.
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.
Following the name of the external application, add the URL used for doing a Google search, up to but not including the search term: http://google.com/search?q=
The text in the Action field should now look like this: firefox http://google.com/search?q=
Click on the drop-down box containing the field names for the lakes layer. It’s located just to the left of the [Insert Field] button.
From the drop-down box, select ‘NAMES’ and click [Insert Field].
Your action text now looks like this:
firefox http://google.com/search?q=%NAMES
To finalize the action, click the [Add to action list] button.
This completes the action, and it is ready to use. The final text of the action should look like this:
firefox http://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:
Figure Actions 2:
Select feature and choose action
When we click on the action, it brings up Firefox and navigates to the URL http://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 a 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" %]')
This menu is specifically created for Map Tips.
It includes a nice feature: Map Tip display text in HTML.
While you can still choose a
Field to be displayed
when hovering over a feature on the map, it is also possible to insert HTML code
that creates a complex display when hovering over a feature.
To activate Map Tips, select the menu option View ‣ Map Tips.
Figure Display 1 and 2 show an example of HTML code and how it behaves in map canvas.
Figure Display 1:
HTML code for map tip
Figure Display 2:
Map tip made with HTML code
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
Simplify geometry option. There is also a global
setting that enables generalisation by default for newly added layers (see
section Opsi).
Figure Rendering 1:
Layer Geometry Simplification dialog
Catatan
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 composer 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 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 composer to export as a raster, but that is an all-or-nothing solution, given that the rasterisation is applied to all layers.
The Metadata menu 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 catalogue. 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 catalogue.
In MetadataUrl, you can define the general path to the XML metadata catalogue. 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.
Figure Metadata 1:
Metadata menu in vector layers properties dialog
When a layer is added to map canvas, QGIS uses by default a random symbol/color to render its features. You can however set a default symbol in Project ‣ Properties ‣ Default styles that will be applied to each newly added layer according to its geometry type.
But, most of the time, you’d prefer to have a custom and more complex style that can be applied automatically or manually (with less efforts) to the layers. You can achieve this goal using the Style combobox at the bottom of the Layer Properties dialog. This combobox provides you with functions to create, load and manage styles.
A style stores any information set in the layer properties dialog to render or interact with the features (including symbology, labeling, action, diagram... settings).
Figure Vector Properties 10:
Style combobox options
By default, the style applied to a loaded layer is named default.
Once you have got the ideal and appropriate rendering for your layer,
you can save it by clicking the Style combobox and choose:
At the bottom of the Style drop-down list, you see the styles set for the layer and the active one is checked. Once you have more than one style defined for a layer, a Remove Current option can help you delete those you no longer want.
Note that each time you validate the layer properties dialog, the active style is updated with the changes you’ve done.
You can create as many styles as you wish for a layer but only one can be active at a time. Combined to layer visibility preset, this offers a quick and powerful way to manage complex projects with few layers (no need to duplicate any layer in the map legend).
Tip
Manage styles from layer context menu
Right-click on the layer in Layers Panel to add, rename or remove layer style. You can also edit feature symbols.
While these styles are saved inside the project and can be copied and pasted from
layer to layer in the project, it’s also possible to save them outside the project
so that they can be loaded in another project.
Clicking the Style ‣ Save Style
saves the symbol as a QGIS layer style file (.qml) or SLD file (.sld).
SLDs can be exported from any type of renderer – single symbol,
categorized, graduated or rule-based – but when importing an SLD, either a
single symbol or rule-based renderer is created.
That means that categorized or graduated styles are converted to rule-based.
If you want to preserve those renderers, you have to stick to the QML format.
On the other hand, it can be very handy sometimes to have this easy way of
converting styles to rule-based.
If the datasource of the layer is a database (PostGIS or Spatialite for example), you can also save your layer style inside a table of the database. Just click on Save Style combobox and choose Save in database item then fill in the dialog to define a style name, add a description, an ui file if applicable and check if the style is the default style. You can add several style in the database. However each table can have only one default style.
When loading a layer in QGIS, if a default style already exists for this layer, QGIS will load the layer and its style. After you modified the layer style, you can Save as Default, creating a new style that becomes the default one or Restore Default style if you’re not satisfied.
Figure Vector Properties 2:
Save Style in database Dialog
Tip
Quickly share a layer style within the project
You can also share layer style within a project without importing a file or database style: right-click on the layer in the Layers Panel and, from the Styles combobox , copy the style of a layer and paste it to a group or a selection of layers: the style is applied to all the layers that are of the same type (vector vs raster) as the original layer and, in case of vector, have the same geometry type (point, line or polygon).