Video narration
You’re in an unfamiliar city. You open your phone… and for a moment, there’s no dot—no fix. So how does GPS figure out your exact spot? Zoom out from the phone to Earth. High above, GPS satellites orbit and constantly broadcast radio signals. Each signal includes one key thing: an exact timestamp—“I sent this at this moment.” Your phone listens. The signals don’t arrive together; one might take a tiny bit longer than another. And because radio waves travel at the speed of light, that time delay turns into distance: distance equals travel time multiplied by light speed. Now the geometry begins. If your phone knows it’s, say, a certain distance from Satellite 1, you could be anywhere on a huge circle—really a sphere—around that satellite. Add Satellite 2, and you get a second distance region. Where those two overlap, your position narrows down to two possible points. Bring in Satellite 3, and the third overlap chooses just one point. That’s trilateration: using distances, not directions, to find where you are. But there’s a catch—your phone’s clock isn’t perfect. A tiny clock error looks like extra distance. So GPS uses a fourth satellite to solve for one more unknown: the phone’s clock offset. With that correction, all the distance regions line up cleanly. Now zoom back into the city. The map snaps a dot right onto the person—location locked—and a route draws itself to the destination, in sync with the real world.