Abstract: A system for determining the closest navigation point to an aircraft utilizes a sphere of influence principle wherein the earth is subdivided into a plurality of geographic areas, for example, one quarter degree squares of latitude and longitude. An identifier such as an index number of the closest navigation point to each square is stored in a look up table. Position information from the navigation system of the aircraft is used to address the look up table to retrieve the appropriate index number which is then used to address a second look up table that contains information defining the closest navigation point.