Modern Mapping

How does a GPS unit know where I am?

Individual Global Positioning System (GPS) units on the Earth receive information from a U.S. military-run system of 24 satellites that circle the Earth and provide precise time and location data. The individual GPS unit receives data from three or more satellites that triangulate its absolute location on the Earth’s surface. If you are carrying such a device, your absolute location is the same as that of the device.

