Cameras and levels in buildings (explained)

When you add a camera to a building, by default, the camera is associated with the default level if one has been specified. Otherwise, the camera is assigned to the first level. However, you can change this and associate the camera with any other level, or several levels at the same time.

More facts:

If no levels are selected, the camera is visible on all levels.
If you add a building on top of a camera already positioned, by default, the camera is associated with all levels.
If you expand the boundaries of a building, so that it covers a camera already positioned, the camera is associated only with the level that is selected.
If you readjust the boundaries of the building, so that it no longer covers the camera, the camera is no longer associated with the building.