The Regional Land-Use Plan (PRAS) is a plan that covers the entire Brussels-Capital Region. You can read all about it on the perspective.brussels website.
You can see on the plan's maps what the general intended use for the various areas in the region is. You can see in a map view how the areas have been arranged into industrial areas, green spaces, mixed spaces and residential areas.
You will also find a great many legal stipulations on the arrangement of the areas. The PRAS was approved by the Brussels government on 3 May 2001 and entered into force on 29 June 2001.
The map of balance of eligible office areas (CaSBA) from the PRAS shows how much office surface area is permitted in residential and mixed areas.
Brussels Planning Office