The present paper discusses topical challenges for a further development of digital cities: recent lines of argumentation in favor of further development of digital cities primarily result from the model theory, the recent planning theory and interdisciplinary applications (e.g. facility management). The findings of the planning theory are to act as a checklist for quality-examinations of activities already performed in the field of "Digital Cities". It has to be focused on the improvement of utilization possibilities of digital cities. The contribution is based on the variety of personal experience with the modeling of digital cities including the experience published throughout the scientific community.