What GPS is
GPS, the Global Positioning System, is a satellite navigation system that lets a receiver work out its exact location anywhere on Earth. Built and operated by the United States government, it relies on a constellation of around thirty satellites orbiting roughly twenty thousand kilometers above the planet. The system is free to use, which is why it is built into phones, cars, watches, and countless other devices worldwide.
Satellites and their signals
Each GPS satellite continuously broadcasts a radio signal containing two key pieces of information: its own precise position and the exact time the signal was sent, kept accurate by an onboard atomic clock. The satellites are arranged so that several are above the horizon from any point on Earth at any moment, giving a receiver enough signals to work with almost anywhere outdoors.
Measuring distance by time
A GPS receiver does not talk back to the satellites; it only listens. By comparing the time a signal was sent with the time it arrives, the receiver calculates how long the signal traveled. Since radio waves move at the speed of light, that travel time reveals the distance to each satellite. Knowing the distance to one satellite places you somewhere on a sphere around it.
Pinpointing your position
Combining distances from several satellites narrows your location to a single point, a process called trilateration. Two satellites leave too many possibilities, three narrow it down, and a fourth is needed to correct the receiver's own clock, which is not as precise as the satellites' atomic clocks. With four or more signals, the receiver can calculate not just latitude and longitude but altitude as well.
What affects accuracy
A phone's GPS is typically accurate to a few meters, but several things can reduce that. Tall buildings and canyons bounce signals, mountains and dense trees block them, and the atmosphere slightly delays them. Indoors, signals often fail entirely. To improve speed and accuracy, phones combine GPS with Wi-Fi, mobile networks, and other satellite systems such as Europe's Galileo and Russia's GLONASS.
The bottom line
GPS works by having a receiver listen to timed signals from multiple satellites, measure how long each took to arrive, and use those distances to pinpoint its location through trilateration. Four satellites give a precise fix of position and altitude. Understanding this explains both why GPS needs a clear view of the sky and how a small chip in your phone can locate you anywhere on Earth.
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See also: What is GPS? Explained, What is NFC? Explained.
Sources
Published date reflects the original event date (2026-10-23). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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