14.3. Setting a label

Labels are textual information you can display on vector features or maps. They add details you could not necessarily represent using symbols. Two types of text-related items are available in QGIS:

• Text Format: defines the appearance of the text, including font, size, colors, shadow, background, buffer, …

  They can be used to render texts over the map (layout/map title, decorations, scale bar, …), usually through the font widget.

  To create a Text Format item:

  1. Open the Style Manager dialog

  2. Activate the Text format tab

     

     Obr. 14.21 Text formats in Style Manager dialog

  3. Press the ^{Add item} button. The Text Format dialog opens for configuration. As usual, these properties are data-definable.

• Label Settings: extend the text format settings with properties related to the location or the interaction with other texts or features (callouts, placement, overlay, scale visibility, mask …).

  They are used to configure smart labelling for vector layers through the Labels tab of the vector Layer Properties dialog or Layer Styling panel or using the ^{Layer Labeling Options} button of the Label toolbar.

  To create a Label Settings item:

  1. Open the Style Manager dialog

  2. Activate the Label Settings tab

     

     Obr. 14.22 Label Settings in Style Manager dialog

  3. Press the ^{Add item} menu and select the entry corresponding to the geometry type of the features you want to label.

  The Label Settings dialog opens with the following properties. As usual, these properties are data-definable.

14.3.1. Formatting the label text

Whether you are configuring a Text Format or Label Settings item, you will be given the following options:

Properties tab	Text format	Label settings
Text
Formatting
Buffer
Mask
Background
Shadow
Callout
Placement
Rendering

14.3.1.1. Text tab

Obr. 14.23 Labels settings - Text tab

In the Text tab, you can set:

• the Font, from the ones available on your machine

• the Style: along with the common styles of the font, you can set whether the text should be underlined or striked through

• the Size in any supported unit

• the Color

• the Opacity

• and Allow HTML Formatting: The HTML formatting option enables the proper rendering of some HTML tags to customize the label. The supported HTML tags are:

  • Color, applicable to text, underline, strikethrough, and overline

  • Font properties (font family, font size, bold and italic)

  In order to use the HTML formatting, you need to provide the HTML code in the Value field. The expression is parsed and any supported HTML tag overrides its corresponding setting in the labels properties. They also combine well with other background, shadow, buffer… properties of labels.

  Below an example of a HTML-based expression and rendering (applies different colors and underline to the same label):

  format(
    '<span style="color:blue">%1</span> ( <span style="color:red"><u>%2 ft</u></span> )',
    title( lower( "Name" ) ),
    round($length)
  )
  

  

  Obr. 14.24 Labeling with HTML formatting enabled

At the bottom of the tab, a widget shows a filterable list of compatible items stored in your style manager database. This allows you to easily configure the current text format or label setting based on an existing one, and also save a new item to the style database: Press the Save format… or Save settings… button and provide a name and tag(s).

Poznámka

When configuring a Label Settings item, text format items are also available in this widget. Select one to quickly overwrite the current textual properties of the label. Likewise, you can create/overwrite a text format from there.

14.3.1.2. Formatting tab

Obr. 14.25 Label settings - Formatting tab

In the Formatting tab, you can:

• Use the Type case option to change the capitalization style of the text. You have the possibility to render the text as:

  • No change

  • All uppercase

  • All lowercase

  • Title case: modifies the first letter of each word into capital, and turns the other letters into lower case if the original text is using a single type case. In case of mixed type cases in the text, the other letters are left untouched.

  • Force first letter to capital: modifies the first letter of each word into capital and leaves the other letters in the text untouched.

• Under Spacing, change the space between words and between individual letters.

• Stretch ratio: allows text to be horizontally stretched or condensed by a factor. Handy for tweaking the widths of fonts to fit a bit of extra text into labels.

• Enable kerning of the text font

• Set the Text orientation which can be Horizontal or Vertical. It can also be Rotation-based when setting a label (e.g., to properly label line features in parallel placement mode).

• Use the Blend mode option to determine how your labels will mix with the map features below them (more details at Režim míchání).

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

• Configure Multiple lines:

  • Set a character that will force a line break in the text with the Wrap on character option

  • Set an ideal line size for auto-wrapping using the Wrap lines to option. The size can represent either the Maximum line length or the Minimum line length.

  • Decide the Line Height: values can be set to be in Millimeters, Points, Pixels, Percentage, or Inches. When line height is set to percentage it is the percentage of the default text line spacing of that font family. Typically 1.2 to 1.5 times the text size.

  • Format the Alignment: typical values available are Left, Right, Justify and Center.

    When setting point labels properties, the text alignment can also be Follow label placement. In that case, the alignment will depend 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.

  Poznámka

  The Multiple lines formatting is not yet supported by curve based label placement. The options will then be deactivated.

• For line labels you can include Line direction symbol to help determine the line directions, with symbols to use to indicate the Left or Right. 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 Formatted numbers option to format numeric texts. You can set the number of Decimal places. By default, 3 decimal places will be used. Use the Show plus sign if you want to show the plus sign for positive numbers.

14.3.1.3. Buffer tab

Obr. 14.26 Label settings - Buffer tab

To create a buffer around the label, activate the Draw text buffer checkbox in the Buffer tab. Then you can:

• Set the buffer’s Size in any supported unit

• Select the buffer’s Color

• Color buffer’s fill: The buffer expands from the label’s outline, so, if the option is activated, the label’s 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. Unchecking the option (while using totally transparent labels) will allow you to create outlined text labels.

• Define the buffer’s Opacity

• Apply a Pen join style: it can be Round, Miter or Bevel

• Use the Blend mode option to determine how your label’s buffer will mix with the map components below them (more details at Režim míchání).

• Check Draw effects to add advanced paint effects for improving text readability, eg through outer glows and blurs.

14.3.1.4. Background tab

The Background tab allows you to configure a shape that stays below each label. To add a background, activate the Draw Background checkbox and select the Shape type. It can be:

• a regular shape such as Rectangle, Square, Circle or Ellipse using full properties of a fill symbol

• an SVG symbol from a file, a URL or embedded in the project or style database (more details)

• or a Marker Symbol you can create or select from the symbol library.

Obr. 14.27 Label settings - Background tab

Depending on the selected shape, you need to configure some of the following properties:

• The Size type of the frame, which can be:

  • Fixed: using the same size for all the labels, regardless the size of the text

  • or a Buffer over the text’s bounding box

• The Size of the frame in X and Y directions, using any supported units

• A Rotation of the background, between Sync with label, Offset of label and Fixed. The last two require an angle in degrees.

• An Offset X,Y to shift the background item in the X and/or Y directions

• A Radius X,Y to round the corners of the background shape (applies to rectangle and square shapes only)

• An Opacity of the background

• A Blend mode to mix the background with the other items in the rendering (see Režim míchání).

• For SVG symbol, you can use its default properties (Load symbol parameters) or set a custom Fill color, Stroke color and Stroke width.

• Draw effects to add advanced paint effects for improving text readability, eg through outer glows and blurs.

14.3.1.5. Shadow tab

Obr. 14.28 Label settings - Shadow tab

To add a shadow to the text, enable the Shadow tab and activate the Draw drop shadow. Then you can:

• Indicate the item used to generate the shadow with Draw under. It can be the Lowest label component or a particular component such as the Text itself, the Buffer or the Background.

• Set the shadow’s Offset from the item being shadowded, ie:

  • The angle: clockwise, it depends on the underlying item orientation

  • The distance of offset from the item being shadowded

  • The units of the offset

  If you tick 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’s item.

• Influence the appearance of the shadow with the Blur radius. The higher the number, the softer the shadows, in the units of your choice.

• Define the shadow’s Opacity

• Rescale the shadow’s size using the Scale factor

• Choose the shadow’s Color

• Use the Blend mode option to determine how your label’s shadow will mix with the map components below them (more details at Režim míchání).

14.3.2. Configuring interaction with labels

Other than the text formatting settings exposed above, you can also set how labels interact with each others or with the features.

14.3.2.1. Mask tab

The Mask tab allows you to define a mask area around the labels. This feature is very useful when you have overlapping symbols and labels with similar colors, and you want to make the labels visible.

Obr. 14.29 Labels settings - Mask tab (with the text sample showing a green background representing another layer being excluded)

To create masking effects on labels:

1. Activate the Enable mask checkbox in the tab.

2. Then you can set:

   • the mask’s Size in the supported units

   • the Opacity of the mask area around the label

   • a Pen Join Style

   • paint effects through the Draw effects checkbox.

3. Select this mask shape as a mask source in the overlapping layer properties Mask tab (see Masks Properties).

14.3.2.2. Callouts tab

A common practice when placing labels on a crowded map is to use callouts - labels which are placed outside (or displaced from) their associated feature are identified with a dynamic line connecting the label and the feature. If one of the two endings (either the label or the feature) is moved, the shape of the connector is recomputed.

Obr. 14.30 Labels with various callouts settings

To add a callout to a label, enable the Callouts tab and activate the Draw callouts. Then you can:

1. Select the Style of connector, one of:

   • Simple lines: a straight line, the shortest path

   • Manhattan style: a 90° broken line

   • Curved lines: a curved line

   • Balloons: a speech bubble surrounding the label and pointing to the feature. It can have rounded corners.

2. For a line-based callout:

   1. Select the Line style with full capabilities of a line symbol including layer effects, and data-defined settings

   2. If curved, you also define:

      • the percentage of Curvature of the connection line

      • and its Orientation: starting from the label to the feature, it can be Clockwise or Counter-clockwise, or Automatic (determining an optimal orientation for each label)

   3. Set the Minimum length of callout lines

   4. Check whether to Draw lines to all feature parts from the feature’s label

   5. Set the Label anchor point: controls where the connector line should join to the label text. Available options:

      • Closest point

      • Centroid

      • Fixed position at the edge (Top left, Top center, Top right, Left middle, Right middle, Bottom left, Bottom center and Bottom right).

   6. Set the Offset from label area option: controls the distance from the label anchor point (where the callout line ends). This avoids drawing lines right up against the text.

3. For a balloon callout, you’d need to set:

   • the Fill style with full capabilities of a fill symbol including layer effects, and data-defined settings

   • the Corner radius of the speech bubble

   • the Wedge width: how large the bubble speech connection with feature’s pointer should be

   • the Margins around the label’s text

4. Set the Offset from feature option: controls the distance from the feature (or its anchor point if a polygon) where callout lines end. Eg, this avoids drawing lines right up against the edges of the features.

5. Set the Feature anchor point for the (polygon) feature (the end point of the connector line). Available options:

   • Pole of inaccessibility

   • Point on exterior

   • Point on surface

   • Centroid

6. Set the Blend mode: controls the blending of the callout.

Under the Data defined placement group, coordinates of the Origin (on the label side) and/or Destination (on the feature side) points of the callout can be controlled. Callouts can also be controlled manually by using the ^{Move Label, Diagram or Callout} tool in the Labeling Toolbar. The start and end points of each callout can be moved this way. The nodes should be highlighted when the mouse pointer is nearby. If needed the Shift Key can be held during the movement. This will snap the point in a way that the angle between the two callout points increments by 15 degrees.

14.3.2.3. Placement tab

Choose the 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

Point labels placement modes available are:

• Cartographic: 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 in supported units, either from the point feature itself or from the bounds of the symbol used to represent the feature (set in Distance offset from). 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.

  • following a Position priority that can 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.

    By default, cartographic mode placements are prioritised in the following order (respecting the guidelines from Krygier and Wood (2011) and other cartographic textbooks):

    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.

• Around Point: labels are placed in a circle around the feature. equal radius (set in Distance) circle around the feature. The placement priority is clockwise from the „top right“. The position can be constrained using the data-defined Quadrant option.

• Offset from Point: labels are placed at an Offset X,Y distance from the point feature, in various units, or preferably over the feature. You can use a data-defined Quadrant to constrain the placement and can assign a Rotation to the label.

Placement for line layers

Label modes for line layers include:

• Parallel: draws the label parallel to a generalised line representing the feature, with preference for placement over straighter portions of the line. You can define:

  • Allowed positions: Above line, On line, Below line and Line orientation dependent position (placing the label at the left or the right of the line). It’s possible to select several options at once. In that case, QGIS will look for the optimal label position.

  • Distance between the label and the line

• Curved: draws the label following the curvature of the line feature. In addition to the parameters available with the Parallel mode, you can set the Maximum angle between curved characters, either inside or outside.

• Horizontal: draws labels horizontally along the length of the line feature.

Obr. 14.31 Label placement examples for lines

Next to placement modes, you can set:

• Repeating Labels Distance to display multiple times the label over the length of the feature. The distance can be in Millimeters, Points, Pixels, Meters at scale, Map Units and Inches.

• A Label Overrun Distance (not available for horizontal mode): specifies the maximal allowable distance a label may run past the end (or start) of line features. Increasing this value can allow for labels to be shown for shorter line features.

• Label Anchoring: controls the placement of the labels along the line feature they refer to. Click on Settings … to choose:

  • the position along the line (as a ratio) which labels will be placed close to. It can be data-defined and possible values are:

    • Center of Line

    • Start of Line

    • End of Line

    • or Custom….

  • Clipping: Determines how the label placement on a line is calculated. By default only the visible extent of the line is used but the whole extent can be used to have more consistent results.

  • Anchor text: controls which part of the text (start, center or end) will line up with the anchor point. Using Automatic anchoring means that:

    • For labels anchored near the start of the line (0-25%), the anchor placement will be the start of the label text

    • For labels anchored near the end of the line (75-100%), the anchor placement will be the end of the label text

    • For labels anchored near the center of the line (25-75%), the anchor placement will be the center of the label text

  • Placement Behavior: use Preferred Placement Hint to treat the label anchor only as a hint for the label placement. By choosing Strict, labels are placed exactly on the label anchor.

Placement for polygon layers

You can choose one of the following modes for placing labels of polygons:

Obr. 14.32 Label placement examples for polygons

• Offset from Centroid: labels are placed over the feature centroid or at a fixed Offset X,Y distance (in supported units) from the centroid. The reference centroid can be determined based on the part of the polygon rendered in the map canvas (visible polygon) or the whole polygon, no matter if you can see it. You can also:

  • force the centroid point to lay inside their polygon

  • place the label within a specific quadrant

  • assign a rotation

  • Allow placing labels outside of polygons when it is not possible to place them inside the polygon. Thanks to data-defined properties, this makes possible to either allow outside labels, prevent outside labels, or force outside labels on a feature-by-feature basis.

• Around Centroid: places the label within a preset distance around the centroid, with a preference for the placement directly over the centroid. Again, you can define whether the centroid is the one of the visible polygon or the whole polygon, and whether to force the centroid point inside the polygon.

• Horizontal: places at the best position a horizontal label inside the polygon. The preferred placement is further from the edges of the polygon. It’s possible to Allow placing labels outside of polygons.

• Free (Angled): places at the best position a rotated label inside the polygon. The rotation respects the polygon’s orientation and the preferred placement is further from the edges of the polygon. It’s possible to Allow placing labels outside of polygons.

• Using Perimeter: draws the label parallel to a generalised line representing the polygon boundary, with preference for straighter portions of the perimeter. You can define:

  • Allowed positions: Above line, On line, Below line and Line orientation dependent position (placing the label at the left or the right of the polygon’s boundary). It’s possible to select several options at once. In that case, QGIS will look for the optimal label position.

  • Distance between the label and the polygon’s outline

  • the Repeating Labels Distance to display multiple times the label over the length of the perimeter.

• Using Perimeter (Curved): draws the label following the curvature of the polygon’s boundary. In addition to the parameters available with the Using Perimeter mode, you can set the Maximum angle between curved characters polygon, either inside or outside.

• Outside Polygons: always places labels outside the polygons, at a set Distance

Common placement settings

Some label placement settings are available for all layer geometry types:

Geometry Generator

The Geometry Generator section allows a user to alter the underlying geometry used to place and render the label, by using expressions. This can be useful to perform displacement of the geometry dynamically or to convert it to another geometry (type).

In order to use the geometry generator:

1. Check the Geometry generator option

2. Enter the expression generating the geometry to rely on

3. If relevant, select the geometry type of the expression output: the label geometry-based settings such as placement or rendering are updated to match the new geometry type capabilities.

Some use cases include:

• Use a geometry which is saved in another field „label_position“

• Use the generated geometry from the symbology also for labeling

• Use the @map_scale variable to calculate distances / sizes be zoom level independent.

• Combined with the curved placement mode, creates a circular label around a point feature:

  exterior_ring(make_circle($geometry, 20))
  

• Add a label at the start and the end of a line feature:

  collect_geometries( start_point($geometry), end_point($geometry) )
  

• Rely on a smoothed line of a river to get more room for label placement:

  smooth( $geometry, iterations:=30, offset:=0.25, min_length:=10 )
  

Data Defined

The Data Defined group provides direct control on labels placement, on a feature-by-feature basis. It relies on their attributes or an expression to set:

• the X and Y coordinate

• the text alignment over the custom position set above:

  • Horizontal: it can be Left, Center or Right

  • the text Vertical: it can be Bottom, Base, Half, Cap or Top

• the text Rotation. Different units can be defined for the labeling rotation (e.g. degrees, minutes of arc, turns). Check the Preserve data rotation values entry if you want to keep the rotation value in the associated field and apply it to the label, whether the label is pinned or not. If unchecked, unpinning the label rotation is reset and its value cleared from the attribute table.

  Poznámka

  Data-defined rotation with polygon features is currently supported only with the Around centroid placement mode.

Poznámka

Expressions can not be used in combination with the labels map tools (ie the Rotate label and Move label tools) to data-define labels placement. The widget will be reset to the corresponding auxiliary storage field.

Priority

In the Priority section you can define the placement priority rank of each label, ie if there are different diagrams or labels candidates for the same location, the item with the higher priority will be displayed and the others could be left out.

The priority rank is also used to evaluate whether a label could be omitted due to a greater weighted obstacle feature.

Obstacles

In some contexts (eg, high density labels, overlapping features…), the labels placement can result in labels being placed over unrelated features.

An obstacle is a feature over which QGIS avoids placing other features‘ labels or diagrams. This can be controlled from the Obstacles section:

1. Activate the Features act as obstacles option to decide that features of the layer should act as obstacles for any label and diagram (including items from other features in the same layer).

   Instead of the whole layer, you can select a subset of features to use as obstacles, using the ^{Data-defined override} control next to the option.

2. Use the Settings button to tweak the obstacle’s weighting.

   • For every potential obstacle feature you can assign an Obstacle weight: any label or diagram whose placement priority rank is greater than this value can be placed over. Labels or diagrams with lower rank will be omitted if no other placement is possible.

     This weighting 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 kind of obstacle the feature is:

     • 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 the boundary of the polygon (prefers placing labels outside or completely inside the polygon). This can be useful for layers where the features cover the whole area (administrative units, categorical coverages, …). In this case, it is impossible to avoid placing labels within these features, and it looks much better when placing them over the boundaries between features is avoided.

14.3.2.4. Rendering tab

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

Label options

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 two 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).

  Poznámka

  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 layers‘ features.

• Allow inferior fallback placements: By default QGIS tries to render labels at their best placement, following your settings. Check this mode to allow features to fallback to worse placement options when there’s no other choice, e.g. when a line is too short to fit a curved label text then the label may be placed horizontally just over the feature’s center point.

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

• Allow to Show upside-down labels: alternatives are Never, when rotation defined or always.

• The Overlapping labels group allows you to control whether overlapping labels are permitted for features in the layer and how each of them should be handled:

  • Never overlap: never ever place overlapping labels for the layer, even if it means some labels will be missing

  • Allow overlaps if required: if the label can’t otherwise be placed, draw an overlapping label. This mode will cause the label to be moved to a less ideal placement if possible, e.g. moving the label further from the center of a line or polygon, IF doing so will avoid overlapping labels. But if there’s no other positions possible, then draw the label overlapping.

  • Allow overlaps without penalty: It doesn’t matter at all if the label overlaps other labels or obstacles, that’s fine to do and the best placement (e.g most central placement) should always be used even if an alternate further placement is possible which avoids overlaps entirely.

  Allowing both overlapping labels and fallback placements options will guarantee that all features in the layer are labeled… not necessarily at their best rendering!

Feature options

Under Feature options:

• You can choose to Label every part of a multi-part features and Limit number of features to be labeled to.

• 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 their 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 the Placement tab.