The Global Positioning System is today used in all forms of navigation like air, surface. It has become a very essential part of them. It is more commonly known as GPS. It was developed by the United State's Defense Department. The department invests $400 million annually to maintain this system.

GPS is a satellite based navigation system. The system uses 24 satellites to indicate the accurate location of any stationary or moving object in the world. The satellites are maintained by the defense department. They transmit signals to GPS receivers all over. The receivers then find their location accurately in terms of altitude, longitude and latitude. Snow or rain does not hamper their function and they continue to work irrespective of the weather.

There are five monitoring station for this system. They are located at Ascension Island, Kwajalein, Colorado Springs, Hawaii and Diego Garcia. However they have to report to the master control station which is located at the Schriever Air Force Base. The 50th Space Wing based at Schriever AFB makes sure that all satellites work properly and give accurate results.

The satellites used in this system are placed at an altitude of 20,200 km and they are placed in such a way that there will always be four satellites in your line of vision no matter where you are. The 24 satellites have been put up in six planes; each plane thus has four satellites. These satellites go round the earth twice daily and send down information regarding their position, and also about the estimated position of other active satellites. After calculations are done, the exact location is given by the receiving set by using the concept of trilateration.

For enhancing GPS accuracy, a number of satellites were added which had a second civilian GPS signal called L2C. This was done in 2005, and in the coming years more satellites will be put which will add the third and fourth civilian signal.

GPS is used in different fields of life. The government doesn't charge anything from people for using this system. Other than navigation, GPS helps in cartography and land surveys. It is also an exceptionally accurate time reference for scientific research and telecommunications.