Advocates a desktop virtual reality (VR) interface to a geographic information system (GIS). The navigational capability to explore large topographic scenes is a powerful metaphor and a natural way of interacting with a GIS. VR systems succeed in providing visual realism and real-time navigation and interaction, but fail to cope with very large amounts of data and to provide the general functionality of information systems. We suggest a way to overcome these problems. We describe a prototype system, called ViRGIS (Virtual Reality GIS), that integrates two system platforms: a client that runs the VR component interacts via a (local or wide area) network with a server that runs an object-oriented database containing geographic data. For the purpose of accessing data efficiently, we describe how to integrate a geometric index into the database, and how to perform the operations that are requested in a real-time trip through the virtual world.