The paper presents a real-time database for modeling complex networks of intersecting roads and walkways in urban virtual environments. The database represents information about the layout of streets and sidewalks, the rules that govern behavior on roads and walkways, and the locations of agents with respect to road and sidewalk structures. This information is used by programs that control the behavior of autonomous vehicles and pedestrians populating the virtual urban environment. Roads and sidewalks are modeled as ribbons in space. The ribbon structure provides a natural coordinate frame for defining the local geometry of navigable surfaces. This geometry is important for way finding and also forms the geometric basis on which spatial relationships among agents are defined. The database includes a powerful run-time interface supported by robust and efficient code for locating objects on the ribbon network, for mapping between Cartesian and ribbon coordinates, and for determining behavioral constraints imposed by the environment.