1. A method for rendering a three-dimensional map using terrain data, comprising the steps of: accessing the terrain data on a computer system; selecting the boundaries of the terrain data to be used to render the three-dimensional map; dividing the boundaries of the terrain data into regular geometric areas; defining a type of free-edged, planar geometric surface; approximating terrain in each regular geometric area, using the defined free-edged, planar geometric surface, as an independent free-edged, planar geometric surface; checking the terrain approximation for each regular geometric area to determine if the terrain approximation is within user selected tolerances; dividing the regular geometric areas outside the user selected tolerances into smaller regular geometric areas and approximating terrain data as described above for each of the smaller regular geometric areas; recursively repeating the checking and dividing steps until all terrain approximations for regular geometric areas fall within user-selected tolerances; and, outputting a final compressed three-dimensional map using final terrain approximations data to a map rendering device.