| A waypoint, as originally used in navigation, pilotage and orienteering, is a map location, optionally with a time coordinate. It is used to denote an interim navigational point along a planned route, typically one where a change of course or a break in travel is planned (or, in the case of a recorded course, logged). It is only used, however, when one is navigating by external reference - in other words, it is based on location not calculation. If one is using dead reckoning, or navigating using an inertial navigation system, course changes are not typically noted as waypoints - since there is an acknowledged error between the calculated position and the 'absolute' position until an exernal reference can be consulted.
With Global Positioning System and similar (GLONASS and soon GALILEO) instruments, a waypoint is a set of coordinates stored in the system (again, optionally with time and comment data) which describe a particular location. When strung together in order, waypoints in such systems will describe a complete journey from origin to destination. Most modern navigation systems can be told to automatically record position at regular intervals, creating waypoints for a 'return to origin' track as well as for recording points visited.
The term 'waypoint' as defined in several places prior to cheap, common navigation systems was restricted to points lying on surveyed routes and trails. It may have arisen from the use of such phrases as 'half way point' or 'quarter way point' in descriptions which placed locations between two other known points.
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