Let's assume I have the floor plan of a multi-apartment house as a background layer. In addition, there is an area layer "Room" highlighting a room in colour if I click on it given outer dimensions of the room as a polygon. Each room is part of a flat whose location field can be composed of all polygons of the associated rooms.
My intention is as follows: By clicking on a room, this room should still be highlighted in colour, but I would like all other rooms in the same flat to be coloured as well (i.e. in grey).
How do I achieve this? I have already tried to insert a new area level, but instead of the whole flat, only the room is coloured (due to the filter selection by clicking on one room).