7-4. Create a categorical constraint

The principle

A categorical constraint works on data made up of discrete coded values — here, the ESA WorldCover land cover classes where 10 is tree cover, 20 is shrubland, and so on. Each value becomes a checkbox in the viewer, and the wind power data is only drawn where the land cover pixel matches one of the ticked values.

The values you enter must match the pixel codes in the constraint COG exactly — the labels are only for display.

Configure it

1. On the Austria Wind Power Density at 100m layer card, click on the Constraints tab.

2. Select Add constraint, keep the source type as Direct URL and paste the WorldCover COG that has been prepared to align with the wind power data:

   https://esa-apex.s3.eu-west-1.amazonaws.com/APEX-example-data/constraints/PowerDensity_100m_Austria_WGS84_COG_clipped_3857_fix-esa_worldcover_2021.tif
   

3. Set:

   • Label — Land Cover (from World Cover)
   • Interactive — on
   • Constraint Type — Categorical

4. Select Populate Categories from COG. The builder reads the distinct values present in the file and creates a row for each one.

5. Edit the labels so they read as class names rather than numbers:

   Label	Value
   Tree cover	10
   Shrubland	20
   Grassland	30
   Cropland	40
   Built-up	50
   Bare	60
   Snow and ice	70
   Permanent water bodies	80
   Herbaceous wetland	90
   Moss and lichen	100

   This is the same class list used in 5-3. Categories from a COG, and is also available as a CSV file.

   Note

   Not every class is present in Austria. Values that the COG does not contain simply never mask anything, so it is harmless to leave them in.

6. Save the constraint.

View the result

Open the Preview. The layer now has a set of land cover checkboxes. Untick everything except Cropland and Grassland — the wind power density is now only rendered over agricultural land, which is a reasonable first pass at where turbines could actually be sited.

Did you remember to export?