Disclosed is a technique for generating a three dimensional terrain map of a geographic area. Mobile units are equipped with satellite receivers (e.g., GPS receivers) for generating location data. A map generator uses the location data to generate a three dimensional terrain map. In one embodiment, the mobile units have primary uses other than mapping, and are traversing the geographic area to be mapped in connection with their primary function. The map generation process may be performed iteratively over time, as additional location data becomes available. During a time period when location data is unavailable for a portion of the three dimensional terrain map, the map generator may estimate the missing portion of the map using the available data. The estimated portion may later be updated with actual data as that data becomes available. The map may also contain enhancements based on enhancement data received by the map generator.