Hello Kristof,
I work with Allplan and haven’t any problem to have several IfcSite in one project, as well as several buildings (IfcBuilding) on every site.
Here is a simple example - one IfcProject, four IfcSite and every IfcSite contains one or two IfcGeographicElement(s). For every IfcGeographicElement I can apply either same properties sets or make them different - its up to my own decision.
Here is a simple example (I didn’t input any special properties here, except Name), below, in IFC4.3.
Regards,
Alexey
TopoSites.ifc (9.9 KB)