How GPS works

Suppose you are at a place and don’t know where you are. You ask someone where I am. He says around 400 km from Nagpur .

This is a nice, hard fact, but it is not particularly useful by itself. You could be anywhere on a circle around Nagpur that has a radius of 400km, like this:

You ask somebody else where you are, and she says, "You are 500 kms from Delhi. Now you're getting somewhere. If you combine this information with the Nagpur information, you have two circles that intersect. You now know that you must be at one of these two intersection points, if you are 400 km from Nagpur and 500 km from Delhi : 

If a third person tells you that you are 600 km from Ahmedabad, you can eliminate one of the possibilities, because the third circle will only intersect with one of these points. You now know that you exactly located at Bhopal.

The same concept works with the GPS satellite system calculates your position dynamically and plots your position on a map. And an accurate location of your vehicle is calculated. 

Three of the 24 GPS satellites orbiting the earth report the current position to your navigation system. At the same time, state-of-the art sensors record every movement, registering even the slightest change of direction. Most roads in the city are stored in the navigation device, a Pocket PC. This means the computer always knows your exact position, and so do you.