The Global Positioning System, usually called GPS, is a satellite navigation system used for determining one's precise location and providing a highly accurate time reference almost anywhere on Earth or in Earth orbit. It uses an intermediate circular orbit (ICO) satellite constellation of at least 24 satellites.

The precision of the GPS signal itself is about 20 meters (65 ft). Using differential GPS and other error-correcting techniques, the precision can be improved to about 10 cm (4 in).

The GPS system was designed by and is controlled by the United States Department of Defense and can be used by anyone, free of charge.

GPS system is used by countless civilians as well, who can use the GPS's Standard Positioning Service worldwide free of charge. Low cost GPS receivers (price $100 to $200) are widely available, often combined in a bundle with a PDA, car computer, or Vehicle tracking system. The system is used as a navigation aid in airplanes, ships and cars. The system can be used by computer controlled harvesters, mine trucks and other vehicles. Hand held devices are used by mountain climbers and hikers. Glider pilots use the logged signal to verify their arrival at turnpoints in competitions. More costly and precise receivers are used by land surveyors to locate boundaries, structures, and survey markers.

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