Explain · analogy · Like I'm five version
How GPS works in terms of a game of Marco Polo
Is GPS just a big game of Marco Polo played with satellites in the sky?
A satellite is like a friend in the pool who shouts Marco. Your phone is like you, waiting to hear the shout so you know where you are. The satellite tells your phone the exact time it sent the signal. Your phone does the maths to see how long that shout took to reach your ears. This tells your phone how far away it is from that friend.
To know where you are standing, you need to hear three different friends shout at once. If one friend says they are far away and another says they are close, your phone draws circles on a map to find the spot where they meet. It is like having three friends calling out from different sides of the garden. Your phone listens to all of them to work out exactly where you are hiding.
Sometimes, your phone hears a fourth friend high above the clouds to make the spot even more perfect. This keeps your blue dot on the screen from jumping into the neighbour's hedge. It is a very fast game, happening over and over again every single second. You never even hear the satellites shout, but they are always playing along so you do not get lost on your way to the park.
Where the analogy breaks downSatellites send signals one way and do not actually listen for your phone to shout back.