GPS is stands for Global Positioning System. GPS is a satellite based system that allows you to know your position anywhere on Earth.
It was developed for the USA military to allow soldiers to know exactly where they were regardless of whether it was day or night, deep in a jungle or in a barren desert. It is still owned and controlled by the USA military.
It makes use of a method called 'triangulation'. You often see this being used in action films where the villains are being tracked on a map as they move about. Tracking a villain.... Imagine that you have a machine that can tell you the distance between yourself and the villain. That's all it can tell you - just the distance. So you draw a circle with you as the centre. The villain is somewhere on that circled line.
Now a colleague also lets you know how far the villain is away from them. So draw another circle around him. So you know that the villain must be at point A or Point B. But which one? So you need a third colleague to let you know their distance and this pinpoints the villain's location. Hence the word 'triangulation' - three measurements can pinpoint a location.
Well, if you can measure the distance between yourself and at least three satellites (preferably four), then your location on Earth can be worked out. How accurately you can pinpoint your location depends on how accurately you can measure the distances to the satellites. Commercial Sat-Nav systems can measure to within a few metres.
It now has a vast number of uses. For example, in cars - satellite navigation systems are becoming common; Lorry Fleets: Used to track and locate vehicles; Military - its original purpose, to help soldiers in the field; Shipping - to navigate the seas; Farming - to track crop growth and fertilizer application; Leisure - Mountaineers, hikers, explorers; Crime - offenders can now be 'tagged' with a GPS device to make sure they stay where they should.
GPS has become so widespread in everyday life, that some regions want to control their own GPS for their citizens. For example the European Union have been developing a similar system called Galileo.
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