Providing an equally sufficient and efficient transit service requires careful planning and permanent monitoring of service quality, operating costs, and revenues. These requirements need a model that is capable of determining impacts on passengers as well as operators. Additionally, it is important to provide suitable and powerful methods to design and to modify the transit network. The transport planning software VISUM attempts to fulfill these requirements. In contrast to conventional Geographic Information Systems (GIS), which are extended to provide specific functionality for transit planning, VISUM is a comprehensive transportation model with additional GIS functionality. It seeks to fill the gap between conventional GIS programs and vehicle scheduling programs.