GPS, or Global Positioning System, is the technology behind ‘SatNav’ that we are now familiar with seeing – not only directing dirt-free urban 4x4s to the nearest car wash but also in modest family cars guiding owners to a new holiday destination or the fastest route to granny’s house.
GPS works with the 24 satellites orbiting this globe(Earth), each constantly sending out electronic messages. A GPS receiver is a small computer device that looks for and listens to these messages, from which it can use trilateration(similar to triangulation) to work out where the receiver is relative to all the satellites.
GPS needs a line of sight with at least 4 satellites to get enough messages to identify a location. Providing you aren’t standing under dense tree cover or in a canyon there will always be 4 satellites visible to a receiver but normally 7-8 to give good accuracy, and even your altitude. GPS receivers only receive the messages from which they work out your location, they don’t send messages so you are not actually being tracked or spied on when you use GPS.
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