How GPS finds your location — Technology, 11–13
GPS does not look down from space and see you. It compares carefully timed signals from satellites to work out where you are on Earth.
The idea
Several satellites send out signals containing the time they were sent. Your phone compares arrival times and uses the differences to estimate its distance from each satellite. Three or more distances can point to one place on a map.
Why it was needed
Maps are useful, but a map cannot know which road you are standing on. Earlier navigation often needed landmarks, compasses or a person reading coordinates. GPS solves the problem of finding a position automatically, even when familiar landmarks are missing.
A worked example
Imagine your phone receives signals from three satellites. The timings suggest you are 20 km from satellite A, 25 km from B and 30 km from C. Draw three circles with those radii on a map: where they meet is your estimated position. Real GPS also corrects clock and signal errors.
The common trap
It is easy to think GPS works because a satellite takes a photograph of you. That seems reasonable because maps show a moving dot, but the dot is calculated from signals, not seen from above. Tall buildings, trees or bad timing can make the estimate wander.
Where it is used
GPS helps a navigation app choose a route and lets an emergency service find a caller’s approximate location. Ships, aircraft, farmers and sports watches use it too. A location is an estimate, so important decisions may combine GPS with maps, radio or other instruments.
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