Global Positioning System- GPS- Amazing  

The Global Positioning System (GPS) is the only fully functional Global Navigation Satellite System(GNSS) Utilizing a constellation of at least 24 medium Earth orbit satellites that transmit precise microwave signals, the system enables a GPS receiver to determine its location, speed, direction and time.
Developed by the United States Department of Defense, it is officially named NAVSTAR GPS. The satellite constellation is managed by the United States Air Force 50th Space Wing. The cost of maintaining the system is approximately US$750 million per year including the replacement of aging satellites and research and development.
A GPS receiver calculates its position by measuring the distance between itself and three or more GPS satellites. Each satellite has an atomic clock, and continually transmits messages containing the exact time,the location of the satellite (the ephemeris), and the general system health (the almanac).
Read more on wikipedia.com
GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is. Now, with distance measurements from a few more satellites, the receiver can determine the user's position and display it on the unit's electronic map.
Today's GPS receivers are extremely accurate, thanks to their parallel multi-channel design.
Read more on www8.garmin.com
We were recently on a trip where we bought GPS as it was very cheap because of Thanksgiving Sale.....lol just $199/- and it made our trip exciting and easy.
No problem of loosing the way and wasting time to get back on track.
If you miss the way or take a wrong turn GPS recalculates and tells you the way where to turn and get back in original path.
I really was impressed with the technology and salutes the mind who even thought about it.
It was not working when we were in parking lot because of network problem and a few friends told it was not working at Downtown Chicago too, may be because of tall building and improper network connection.
Else the technology is best and its must if you are on road to a new city.
Have you ever used GPS, share you views and opinions.