Gps position is derived by intersection of several circles obtained from satellites orbiting the earth at an altitude of 20,000 km. There are a total of 30 satellites used for GPS Navigation. The technology was originally developed by US Government for military navigation.
The GPS position results are obtained by a trilateration method. At any position on the earth the GPS device can be accessed by a minimum of 4 satellites. These satellites have atomic clocks on board. Meanwhile the GPS device calculates the distance from each of the satellites. The device makes circles of the obtained distance from the satellites. The coinciding point of atleast 3 circles is the final position of the device.
Source: www.physics.org
