The residential polygon was imported from CLC (Corine Land Cover) from 2006. These polygons are not very accurate due to the low quality imagery that was used at that time.

> Wiki says "landuse=residential" is also valid for mixed industrial/living areas. This would be hard to decide from aereal imagery only, therefore I hesitated to touch it. 

In Bulgaria there is no such thing as mixed industrial and living area. It's either one or the other. Living areas (small strangely shaped buildings, very little paved area, a lot of greenery) are quite distinct compared to industrial areas (big boxy buildings, large paved areas). There are also farmyards which can be recognised by the long rectangular buildings, silos and agricultural equipment.