Now each building has the name and surface area of the neighbourhood to which it belongs.
In order to calculate the building density, we need to calculate the total surface area of the building in each neighbourhood. Therefore, we first need to dissolve the building polygons, based on their neighbourhood name attribute.
1. In the main menu, choose Vector | Geoprocessing Tools | Dissolve....
2. In the Dissolve dialog, choose buildings with neighbourhoods as Input layer, choose buurtnaam as the Dissolve field and save the result to the GeoPackage with the name buildings dissolved.
3. Click Run. Click Close after processing has completed.
Let's check the result visually.
4. In the Layers panel, select the buildings dissolved layer.
5. Go to the Layer Styling panel.
6. Change the Single Symbol renderer to Categorized. Choose buurtnaam for Value.
7. Click Classify.
Now all buildings of the same neighbourhood have the same random colour.
