City modelling is a topic which has been on the agenda for a long time and two main approaches from different angles in this field can be identified. GIS experts have attempted over the years (in collaboration with programmers) to build information systems for cities by means of combining graphical information with related metadata. Architects also started to get involved in this field. However, they were mainly interested in the spatial aspects of a city model and created their own “city models” for different purposes. Today crucial questions concerning the creation itself are resolved, the vision of implementation into daily work becomes more and more important. In other words: “what to do” with the accumulated data. This paper intends to identify the core role of the architect in the field of 3D-city modelling.