Abstract: A ground proximity warning system utilizes geographic position data to alter the warning criteria as is required by the terrain features of particular geographic areas. To determine whether the aircraft is within a particular geographic area, the world is subdivided into latitude bands that are in turn subdivided into non-overlapping zones by predetermined lines of longitude, with the position of each zone being defined by the latitude and longitude coordinates of one of its corners. The zones are further defined by regions which may overlap other zones. The regions are limited in size, and their positions are also defined by the locations of one of their corners. The regions are further subdivided into one or more geographic areas that are defined by their shapes and locations within the region.