Some facts about the global positioning system

Chances are that you have used a global positioning system enabled device before. Maybe it was in the car or maybe using a handheld system. GPS allows you to find your current location anywhere on earth and with some software added also to get directions how to get to anywhere else.
GPS started as a military system allowing the US army to pinpoint where its soldiers and vehicles are. But the GPS system was opened up for civil use too although up to a few years ago the resolution of the location discovery was limited.
With GPS becoming more and more pervasive it was became cheaper. Today you can buy a fully equipped GPS device for a few tens of dollars. And with low memory prices devices costing around two or three hundred dollars can have detailed maps covering all the united states and a nice LCD screen to display them.
The GPS system is comprised of a large number of satellites that were positioned in specific and accurate orbits. The GPS device core is a receiver and an antenna. Old GPS devices needed a large antenna to receive the satellite but with improvements in electronics resulting in more sensitive receivers the new GPS devices antennas are small and in most cases are simply built into the device.
The GPS device receives a signal from a few satellites concurrently. The GPS knows at any given point in time where each satellite is positioned and the distance to that satellite. By calculating the intersection between the different satellite spheres the GPS can know the exact position altitude, longitude and latitude. By correlating this information with detailed map files and the GPS its location on a map. And add some sophisticated software and the GPS can calculate directions and continually track where it is and correct the directions as its position changes.
GPS devices can also calculate speed by simple measuring the time passed to move from one location to another. GPS devices are a commodity today and they are used both by consumers in cars or handheld but also in commercial systems like airplanes and ships. GPS works in any weather condition and needs very little energy to operate.
Some GPS devices today are so small that they can fit in a wristwatch or a cell phone. Many people confuse between the GPS ability to determine its location to all the other goodies like color maps and driving directions. In fact the only thing the global positioning system does is calculate a location on earth. Once that was calculated the rest is a specific application that uses this information together with routing software and maps to provide driving directions. But there are many other applications for example GPS devices are placed in strategic places on the north pole to measure icebergs movements or GPS devices. Other GPS devices are used on vehicle fleets to manage where each truck is or on taxi cabs allowing a central reservation system to find the closest taxi to the passenger order one.

Source: http://www.therealarticles.com/Article/Some-facts-about-the-global-positioning-system/147444