The latest easily available system for finding your location goes under the acronym GPS, which stands for Global Positioning System. It is common for GPS systems to be placed within cars, but handheld portable devices are not rare either. In fact you can now buy cell phones which are GPS enabled. They work on a very simple principle; they take four points of known location and measure the distance between them and the GPS. The four points of known location are actually satellites that are orbiting the Earth.

The satellites are constantly sending signals which the GPS receives. Each satellite sends the signal at exactly the same time but because they are at different distances from the GPS they arrive at the device at different times. The GPS can establish how far it is from each satellite based on the time it took for the signal to reach the device. It then deciphers the information from all the signals to pinpoint the location on Earth.

The device, having identified how far away it is from the satellite knows that its location is one of an infinite number on the surface of a sphere with the satellite as the central point. By taking readings from a number of satellites, it knows it is at a point on the surface of all four of the satellite spheres. To identify its location, the device looks for the point where all four spheres intersect.

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