A child in a park holds a phone beneath three distant colorful satellites.

How does your phone know exactly where you are?

choose a satellite →

Your phone must choose the one map spot where you are. Satellites cannot see you, so it has to collect clues and rule out the wrong spots.

First, make one “how far?” clue. A satellite sends a signal that says when it left. Your phone checks when it arrives: more travel time means more distance.

A golden signal crosses the park from a blue satellite to a green phone beside a clock.

Try it: send the signal. When it reaches the phone, the phone learns how far it is from the blue satellite — but not which direction.

Now draw that clue on a simple flat map. One distance cannot choose one dot: every grey phone spot on the blue ring is exactly that far from the satellite.

One satellite distance leaves a whole ring of possible phone spots A blue satellite sits in the center. Six identical grey phones sit on one blue circle, all the same distance away.

Drag from CLOSE to FAR. You are changing the distance measured from the signal; the blue ring redraws every map spot that could still be your phone.

measured distance: medium
CLOSEFAR

Possible phone spots: still a whole ring.

One distance still leaves a whole ring. So the phone asks a second satellite for another “how far?” clue. Before its green ring appears, guess what two clues will leave.

A child watches one blue distance-ring while a second green satellite prepares another clue.

Flat-map test: the rings cross; they do not just touch.

When this second ring crosses the first, how many map spots fit both distances?