How GPS works: how your phone knows where you are
GPS with no phone signal: why the dot on your map still moves
High on a mountain, your phone shows no signal and no internet. Yet the blue dot on your map follows every step you take. Something is talking to your phone. Who is it, and does it know you are there?
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1
You and your friend Rono are hiking up to a mountain hut, where Miva waits for you. Up here, your phone has no signal at all. Still, on the map you saved last night, the dot moves with every step you take.
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2
Rono points up at the sky. No phone mast can hear you up here. So who is following your steps?
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3
He is right to point up. About 30 GPS satellites go around the Earth, about 20,000 km above it. Each one goes once around the Earth in 12 hours. They are spread out, so several of them are always above the mountain.
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4
Each satellite does one job, again and again. It sends a radio signal down to everyone below it. The signal says which satellite it is, where it is, and the exact time.
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5
Your phone does not answer. It only listens, like a radio. That is why it needs no phone signal, and why any number of phones can listen at the same time.
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6
So the satellites have no idea that you are here. Your phone must find its own place from what it hears. And all it hears is a few satellites saying the time and where they are. Nothing in that says where you are.
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Quick check
A thousand hikers open their maps on the same mountain, at the same moment. Does GPS get slower for them?
Show the answer
No. The satellites send the same signal to everyone and hear nothing back. One phone or a million phones makes no difference to them.
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Go further
A few words to search for.