The Global Positioning System is a constellation of satellites orbiting earth twice daily, transmitting time and position (latitude, longitude and altitude) information. With a GPS receiver, you can determine your location anywhere on Earth.

The complete system consists of 24 satellites orbiting about 12,000 miles above the Earth, and five ground stations to monitor and manage the satellite constellation. These satellites provide 24-hour-a-day coverage for both two- and three-dimensional positioning anywhere on Earth.

Development of the $10 billion GPS satellite navigation system began in the 1970's by the Department of Defense, which continues to manage the system, to provide continuous, worldwide positioning and navigation data to military forces around the globe. GPS has even broader civilian and commercial applications. So GPS offers two levels of service, one for civilian access and second encrypted for military use. The GPS signals are available to an unlimited number of users simultaneously.