For the subsequent calculation of areas, the software provides the grouping of rooms to form apartments. Apartments are not really layers as such, so they can not be set to visible or invisible over the project viewer, although the tree structure appears to allow such functions. Apartments can consist of rooms from different floors but not from different buildings. The properties dialog for apartments can be activated when a building is selected in the tree structure in the same way as for creating new floors. The dialog presents all rooms in the current building, with their names and the floor they belong to, and they can then be assigned to an existing apartment or used to create a new one. Newly created rooms can also be assigned to an existing apartment over the ‘Room’ dialog.