Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. A Waypoint is a reference point in physical space used for purposes of navigation. WAypoints are sets of coordinates that identify a point in physical space. FOr the purposes of terrestrial navigation, these coordinates usually include longitude and latitude, and sometimes altitude (particularly for air navigation). WAypoints have only become widespread for navigational use by the layman since the development of advanced navigational systems, such as the Global Positioning System (GPS) and certain other types of radio navigation. WAypoints located on the surface of the Earth are usually defined in two dimensions (e.G., longitude and latitude); those used in the Earth''s atmosphere or in outer space are defined in at least three dimensions (four if time is one of the coordinates, as it might be for some waypoints outside the Earth).