what is global positioning system GPS?

GPS is a satellite network launched from USA government. In the first time, project was started as a military one, to help the track down nuclear explosions and have coordinates of military people on earth. We have more than 30 satellites in the sky now. System is open to civil too and we can track down ourself using GPS handeld pc or GPS car systems. We use them to navigate and find the correct way to reach a city. Modern systems have maps of the nation you are in, and helping with satellite signals, lets you find your way through all the roads. I have a GPS handeld pc, I can localize myself even when I walk or go in bycicle :). Of course I use it when I drive my car, and it's really nice, it speaks with a female voice and guide me through all roads I must go to reach a point I select on it and an address I want to reach!