Qgis point labelling

# On automatic labelling

I’ve yet to find a good automatic labelling engine in any software. A automatic labelling engine is a program which automatially arranges labels according to a set of rules. These rules typically include biases against overlap with other labels, intersection into certain geometries, or automatic label sizing and letter spacing. You’ll find labelling engines not only in GIS software but also in games such as the grand strategy titles of Paradox Interactive or even Rimworld. But in the case of games, these often have very primitive labelling engines only cappable of displaying a certain type of label on pre-rendered or currated geometries.

When making a complex map with a lot of features and labelled properties the QGIS labelling algorithm is just unable to keep up. It is often unable to find the most optimal location to place their labels and if features are packed too tight it might just give up and not display your label. You can try this out yourself by loading up the Natural Earth populated places layer, activating labels, and zooming out.

# Manual labelling

This method of labelling is perhaps more accurately described as semi-manual labeling. In software such as Photoshop and Inkscape the user is, after all, expected to manually create text boxes and type out all place names one-after-one. Never so in QGIS where labelling data already probably exists to be tapped into by the label symbology.

When working with point labelling in QGIS I like to disable most features of the labelling engine which you can do in two simple steps:

1. Navigate to the symbology layer of the point feature you’re working with and enable labels like normal. Now enter the ‘Placement’ tab, it is the one next to the rightmost one in the labelling menu. Go to the bottom of this panel and disable ‘Features act as obstacles’ setting.
2. Next, go to the rightmost tab called ‘Rendering’ and change the ‘Overlapping labels’ drop-down-menu setting to ‘Allow Overlaps without Penalty’.

This will disable most features of the labelling engine on this particular layer. You’ll want to repeat this process on other layers or labels if need be.

Now without the labelling engine your labels will overlap each other and other features without any rhyme or reason. We can now start to manually adjusting the positioning of the labels. If you have not done any manual labeling before you may need to enable the labeling toolbar, you’ll find it at the ‘View’ dropdown menu, > ‘Toolbars’ > ‘Label Toolbar’. A new set of tools will now appear on the toolbar. You can hover over these tools to learn more about them and most of them have pretty self-explanatory names.

The most important tool for us is the ‘Move a label’ tool. Click it, make sure your layer is in edit mode, and click any label in your layer. A prompt asking about key joining will appear and it will most likely already be set to fid, id, or something similar, click ‘OK’. What just happened is that the project just created a auxiliary storage table. This is a form of virtual table attached to the project and linked to your layer through the fid. So if feature Madrid has the fid of 21, the auxiliary table is able to pair the data it stores for that fid.

What does this auxiliary storage table contain? It now contains two fields for the x- and y-coordinate for the label of the feature, your point and label now have coordinates independent of each other. If you continue using the ‘Move a label’ tool you can now move labels, wherever you place them, information about the labels new coordinate gets automatically added to the auxiliary table.

Remember that the auxiliary table is tied to the project and not the layer. This means that if you open the layer in another project the label coordinate data will not follow it. There are ways of exporting the auxiliary data but I will not cover that here.

# Making labels follow the graticule automatically

You may have noticed that there is a tool to rotate the labels right next to the move tool. You may be tempted to use it to make the labels follow the latitudal graticule lines, but this process can be automated. For this to work you need to make sure that your layer has the same projection as the one you want to work in. The standard automatic on-the-fly reprojection will make this not work.

Navigate to your layers label panel and go to the placement tab. Scroll down to the ‘Rotation’ option and change the dropdown option to ‘Radians’. Click the little ‘Data-defined override’ context menu and click ’edit…’. Paste this into the expression builder:

coalesce(
  "auxiliary_storage_labeling_labelrotation",
  coalesce(
      azimuth(
      make_point(
        "auxiliary_storage_labeling_positionx",
        "auxiliary_storage_labeling_positiony"
      ),
      make_point( [north pole x-coordinate], [north pole y-coordinate])
    )
  )
)

This code basically makes it so that if you don’t explicitly define the label rotation with the rotation tool, the label will automatically orient towards the north pole. You’ll need to input the cartesian coordinates for the north pole in your projection for this to work. You can get them by finding the rought location of the north pole on your map and clicking ‘Copy Coordinate’ > ‘Map CRS’