How GPS Knows Where You Are

Your phone finds its location by listening to a chorus of satellites and doing timing maths, not by being 'seen' from space. Each GPS satellite constantly broadcasts a message that says, in effect, 'I am satellite 7, and it is exactly this time'. Your phone knows where each satellite is, and by comparing the timestamp to its own clock, it works out how long the signal took to arrive, and therefore how far away that satellite is. One distance puts you somewhere on a huge sphere. Two spheres narrow you to a circle. Three or four intersecting spheres pin down a single point: your position. Because the signals travel at light speed, tiny timing errors mean big distance errors, so the satellites carry atomic clocks and even correct for Einstein's relativity. Precise time is really the secret ingredient of knowing 'where'.