You don’t pay for it and there is no sim card but yet somehow you see your car icon move on a map?
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So the map itself is stored locally on your device. So it just needs to work out where to put you on that map. It receives signals from satellites, and uses that data to calculate where you are.
You’ve probably heard of something called triangulation. So basically, a satellite screams out saying “THE TIME IS 18:02:34.568 RIGHT NOW”. Your SatNav receives that signal and compares it with its own clock. Let’s use simple numbers to make the maths easier. Your SatNav receives the signal 1 second after it was sent. It knows that the signal travels at 1km per second, so therefore you must be 1KM from the satellite.
However, that alone doesn’t tell you where you are, because that satellite could be in any direction. So it does the same thing with multiple satellites, and eventually says “Well if I’m x distance from this satellite, y distance from this other satellite, and z distance from this other satellite, I must be here”. 3 is the minimum required for an accurate result, hence “triangulation”.
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