In geographic information science, a datum provides the frame of reference for the specification of location or position. Typically, location is expressed in terms of point coordinates such as latitude and longitude. For example, the location of a point may be given by the coordinates 144° east longitude, 37° south latitude. However, without explicitly stating the frame of reference or datum relative to which these coordinates have been defined, the specified location is incomplete and ambiguous. Since coordinates are dependent on the underlying datum, the concept of datum becomes vitally important for those involved in the collection, manipulation, analysis, and presentation of geographic information. Failure to understand and appropriately deal with the datum issue can cause many problems, particularly when attempting to integrate data from ...