Do you use GPS?

The Global Positioning System (GPS) is a U.S. space-based radionavigation system that provides reliable positioning, navigation, and timing services to civilian users on a continuous worldwide basis -- freely available to all. For anyone with a GPS receiver, the system will provide location and time. GPS provides accurate location and time information for an unlimited number of people in all weather, day and night, anywhere in the world.

The GPS is made up of three parts: satellites orbiting the Earth; control and monitoring stations on Earth; and the GPS receivers owned by users. GPS satellites broadcast signals from space that are picked up and identified by GPS receivers. Each GPS receiver then provides three-dimensional location (latitude, longitude, and altitude) plus the time.

Equipped with these GPS receivers, users can accurately locate where they are and easily navigate to where they want to go, whether walking, driving, flying, or boating. GPS has become a mainstay of transportation systems worldwide, providing navigation for aviation, ground, and maritime operations. Disaster relief and emergency services depend upon GPS for location and timing capabilities in their life-saving missions.

The addition of GPS hardware to cellular phones has created many advantages, along with some problems. First and foremost is what is called E911, or Enhanced 911. The traditional 911 system used by landlines is for emergency situations, where time is of the essence.

Global Positioning System Overview from The Geographer's Craft at University of Colorado

Diagram of GPS "segments" from EPA page on how Army used GPS tocontrol infestation of June bugs.

System Description:
GPS has three 'segments':

1. The space segment now consists of 28 satellites, each in its own orbit about 11,000 nautical miles above the Earth.
   
   
2. The user segment consists of receivers, which you can hold in your hand or mount in your car.
   
   
3. The control segment consists of ground stations (five of them, located around the world) that make sure the satellites are working properly.

The Defense Department made GPS available for non-military purposes, with some restrictions. On May 1, 2000, President Clinton lifted the restrictions, and announced that the option to degrade civil GPS signals during emergencies would be phased out by 2010. The federal government is committed to providing GPS technology for peaceful uses on a worldwide basis, free of charge.

GPS.gov