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Global Positioning System (GPS)

The Global Positioning System GPS is a satellite navigation system used for determining one's precise location anywhere on Earth. The system is an intermediate circular orbit satellite constellation of 24 satellites. Many refer to the system as the NAVSTAR GPS - Navigation Signal Timing and Ranging Global Positioning System.

The more satellites used the higher the accuracy of location. 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 4 inches or less. If desired GPS surveys can provide sub-centimeter accuracy.

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. The GPS system is divided into three segments: space, control and user. The space segment comprises the GPS satellite constellation.

The control segment comprises ground stations around the world that are responsible for monitoring the flight paths of the GPS satellites, synchronizing the satellites' onboard atomic clocks, and uploading data for transmission by the satellites. A GPS receiver decodes time signal transmissions from multiple satellites and calculates its position by trilateration.

The cost of maintaining the system is approximately US$400 million per year, including the replacement of aging satellites. The first GPS satellite was launched in February 1978, and the most recent launch was in September 2005. The oldest GPS satellite still in operation was launched in February 1989.

To learn more about GPS please read our GPS mapping page.

If you would like to request GPS mapping please fill out the online form.