Geological data provide an essential source of information for space planning in the subsurface. Three-dimensional geological models make this information about the subsurface available for various users and use cases. There is a significant demand for subsurface information in city planning, including the modeling of buildings and infrastructures. This demand arises from the interaction between geological processes and the (potential) use of the underground. The paper introduces a concept of a voxel model that includes buildings, traffic infrastructure and the geological structure of the subsurface. The voxel modeling approach aims to provide a unified visualization of geological and urban modeling elements. Furthermore, an analysis of the interaction between buildings and their environment, characterized by geological properties, such as strength of the construction ground or hydraulic and heat conductivity should be feasible. Finally, this paper discusses the feasibility of the concept, based on a case study for the city center of Stuttgart, Germany.