✦ The science, made simple
How does GPS actually work?
Your phone shows a blue dot and you trust it completely. Behind that dot sits a quiet piece of everyday magic: a network of satellites, a ground crew that never sleeps, and a little geometry. Here is the whole story, without the jargon.
GPS is one member of a bigger family called GNSS (Global Navigation Satellite Systems). The idea behind all of them is the same: satellites in space broadcast where they are and what time it is, and a receiver on the ground uses those messages to work out its own position. To see how, it helps to split the system into three parts.
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How three distances become one location
One satellite tells you only that you are somewhere on this circle. Not very useful yet.
Why GPS needs four satellites, not three
Three distances are enough to pin a point in space. The catch is timing. A signal travels at the speed of light, so a tiny clock error becomes a huge distance error. Satellites carry atomic clocks, but your receiver does not.
The fix is elegant: a fourth satellite gives the receiver one more equation, which it uses to solve for the exact time as well as position. With four satellites in view, a cheap receiver effectively borrows atomic-clock accuracy. More satellites then sharpen the result.
From signal to street
How a distance turns into a location
Each satellite stamps its broadcast with the exact moment it left. Your receiver notes the moment it arrived. Multiply that travel time by the speed of light and you get the distance to that satellite. Do it for four satellites and only one point on Earth fits all four distances at once. That point is you.
This method is called trilateration, and it is often confused with triangulation. The difference matters: trilateration uses distances, triangulation uses angles. We break that down in a dedicated guide below.
What makes GPS more or less accurate
A modern phone is usually accurate to a few metres outdoors. A few things push that number around:
- The sky view. Open fields are easy. City streets bounce signals off buildings (multipath), and tunnels block them entirely.
- The atmosphere. Signals slow slightly as they pass through the ionosphere, which receivers correct for using extra signals.
- The receiver. Survey gear using RTK or DGPS reaches centimetre accuracy. Your phone trades precision for size and price.
New tools you can find in our GPS glossary explain the rest.
GPS is not the only one up there
Most modern receivers listen to several constellations at once, which is why your phone locks on so quickly. These are the big four.
GPS
United States
The original, run by the US Space Force.
GLONASS
Russia
Full global coverage, strong at high latitudes.
Galileo
European Union
A civilian-run system with high accuracy.
BeiDou
China
Global since 2020, with a large constellation.