(Canadian Differential GPS) A system of earth stations and one communications satellite that improves the tracking accuracy of the GPS navigation system to less than three feet. It is used for land-based navigation and not aviation. Initiated in 1998, CDGPS, also known as "GPS-Correction" (GPS-C), comprises a group of more than 30 reference stations and one geostationary satellite that covers Canada, the U.S. and Mexico. The stations track the GPS satellites and send correction signals to the CDGPS satellite, which transmits them to CDGPS-enabled receivers. See GPS augmentation system and GPS.