How does GPS know where you are?

GPS works because your phone compares time-stamped radio signals from several satellites. Each signal says where that satellite was and when it left. By measuring tiny travel-time differences, the phone works out its distance from each one, then uses four satellites to correct clock wobble and place you on Earth.

The lovely part is that your map dot is really a measurement of time. A mistake smaller than a blink can mean a huge miss, so the system depends on atomic clocks, light-speed signals, and triangulation: geometry doing careful work while a child wonders which way to turn.