What is GPS?
In one sentence: Global Positioning System: about 31 satellites that broadcast the exact time, so a receiver can work out where it is.
A little more
GPS is a group of about 31 satellites, roughly 20,200 km up, each circling the Earth twice a day. They constantly broadcast where they are and the exact time. A phone or sat-nav that hears four or more can work out its own position, usually to within a few metres under open sky.
GPS only sends; it never receives. The satellites don't know who is listening. Europe's Galileo, Russia's GLONASS and China's BeiDou work the same way, and most phones listen to several of them at once.
It's a bit like… Lighthouses that flash the time instead of a light: anyone can look, and the lighthouse never knows who saw it.
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