Explain · analogy · Serious version
How GPS works in terms of a game of Marco Polo
GPS determines your position on Earth by measuring the time it takes for signals to travel from multiple satellites to your device.
Think of your phone as a person playing Marco Polo in a dark swimming pool, while four satellites act as blindfolded friends shouting from the tiled edges. When you request your location, each satellite broadcasts a precise timestamp indicating exactly when its signal left orbit. Your phone compares this transmission time with the moment the signal arrives, calculating the distance based on the speed of light. It is a game of sonic triangulation where the distance between you and each friend is determined by how long it takes their voice to reach your ears across the chlorinated expanse.
Because light travels at a constant velocity, those tiny intervals allow your phone to draw imaginary spheres around every satellite. Where these four invisible bubbles intersect is your precise coordinate on the map. It is quite elegant, assuming your friends are incredibly punctual and not distracted by a bag of salted crisps. If three friends provide a radius, the fourth friend is strictly required to synchronise the atomic clocks, correcting any drift that would otherwise leave you wandering into the deep end of the leisure centre by mistake.
Without these multiple reference points, your phone would be as lost as a tourist trying to find a specific platform at Clapham Junction. Accuracy relies on these satellites maintaining a perfect, celestial formation, effectively shouting their names in unison so you can navigate the suburbs without resorting to a paper map. It is quite a sophisticated performance for a pocket device that mostly uses its processing power to show you pictures of strangers' labradors.
Where the analogy breaks downSatellites do not actually shout, and you receive data rather than playing a turn-based game.