OpenCities Map contains tools to work with MicroStation 3D solid objects, primarily for urban modeling. These tools convert solids to 3D polygon features and back to solids. 3D polygon features can be polygon collections. To properly represent these 3D polygon features:

1. The feature must a polygon collection.

2. Toggle on the Lock mode for the Delete to Parent propagation rule.

   
   
   

   This way, the operation of this lock can be adjusted during editing by using the Graphic Group lock.