Labels with callout lines in QGIS
UPDATE: As of October 2019, QGIS 3.10 has built-in support for label callout lines!
Callouts, sometimes called leader lines, are lines between labels and features on a map. They are useful when constraints of space force a label to be moved away from the feature. The callout helps to reconnect the label to the feature it refers to.
There are probably multiple ways to do this, but here is one way using a geometry generator in QGIS 3.x:
1. Turn on labels for the layer
- Style dock > Labels tab
- Change "No labels" to "Show labels for this layer"
- Select the field to "Label with"
2. Move individual labels
The upgrade to QGIS 3.0 has made label placement easier to customize. When you move a label, QGIS tracks the new location using hidden auxiliary storage fields that we'll use to draw the lines.
- Make sure the Label Toolbar is enabled (View menu > Toolbars)
- Select the "Move Label" tool
- Click and drag the to move the labels. (The first time you click to move a label, you will be asked for a primary key to use for tracking the labels. Pick a field that has an id or otherwise unique values within your layer.)
3. Add the callout lines
- In the layer styling dock, click the green
+to add a new marker component
- Set "Symbol layer type" to "Geometry generator"
- Set "Geometry Type" to "LineString / MultiLineString"
- Enter the following expression:
make_line( make_point($x, $y), make_point( "auxiliary_storage_labeling_positionx" , "auxiliary_storage_labeling_positiony" ) )
4. Improve the label display
- Add label buffers ("halos") so that the lines won't obscure the text of the label (3rd tab in the style dock)
- Adjust the label placement (6th tab in the style dock), data defined > alignment
- set the horizontal alignment to 'Center'
- set the vertical alignment to 'Half'