Updated: March 2026
GPS is a satellite-based positioning, navigation and timing system. Its job is to determine the user’s position, plot a route and provide the exact time. GPS.gov describes GPS as a US-owned PNT service – positioning, navigation and timing. For civilian users, access to GPS is free and global.
From the user’s point of view, the answer is simple: GPS helps you work out where you are and which way you’re heading. You use it in your phone, your sat nav, your sports watch, your GPS tracker and in many transport systems.
What is GPS?
GPS, or the Global Positioning System, is a system based on satellites and control stations on Earth. It consists of three segments:
- the space segment – the satellites,
- the control segment – the monitoring and management stations,
- the user segment – the GPS receiver in your phone, car, watch or tracker.
That’s exactly how GPS.gov describes it.
In practice, you don’t need to know the whole infrastructure to use GPS. All you need is a device with a receiver that can read the satellite signal and convert it into a position on the map.
How does GPS work?
GPS works by measuring the distance between the receiver and the satellites. The receiver in your phone, watch or tracker picks up signals from the satellites and uses them to calculate its position. This process is based on trilateration – determining a position from known points and the distances to them. GPS.gov explains that it comes down to establishing a position on Earth by knowing where the satellites are and the distance between them and the receiver.
To determine its position accurately, the receiver needs a signal from at least four satellites. This allows it to calculate latitude, longitude and altitude, and to correct the receiver’s clock error. That’s why GPS doesn’t work well when the signal is obstructed or too weak.
What does the GPS system consist of?
The GPS system has three basic parts: the satellites, the control segment and the users’ receivers.
According to GPS.gov, the nominal constellation comprises 24 operational satellites, and the system maintains global coverage thanks to the appropriate positioning of satellites and ground control stations. The number of active satellites can be greater than the nominal constellation.
This matters, because many articles confuse “how many satellites GPS has” with “how many satellites are operational at any given moment”. For the user, what matters more is that the system has global coverage and works around the clock.
How does GPS work in a phone?
GPS in a phone doesn’t rely on satellites alone. Modern smartphones combine data from GPS, Wi-Fi, the mobile network and sensors. Android states this explicitly: the Fused Location Provider combines signals from GPS, mobile masts, Wi-Fi and sensors to determine a more accurate location indoors and outdoors.
This means that when you ask how GPS works in a phone, the answer is: the phone uses GPS, but it refines the result with additional data sources. That’s why location on a smartphone can work faster than on old, basic GPS receivers.
What affects GPS accuracy?
GPS works best under an open sky. GPS.gov states that accuracy depends on factors including satellite geometry, signal obstruction, atmospheric conditions and receiver quality. For smartphones, typical accuracy under an open sky is around 4.9 m, but near buildings, bridges and trees the result is worse.
The most common reasons for poorer GPS performance:
- signal interference.
- tall buildings,
- a tunnel or underground car park,
- dense forest,
- a weak receiver,
- an older device,
How does GPS work in a tracker?
A GPS tracker receives its position and passes it on to an app or monitoring platform. GPS itself is responsible for establishing the coordinates, but for the user to see the device on a map, the tracker usually also needs a data transmission channel, such as GSM/LTE or another way of sending its position.
This is important, because many people confuse GPS alone with a complete tracking system. GPS establishes the position, but it doesn’t “send it to your phone by itself” without additional connectivity.
How does GPS work in a car?
GPS in a car is used mainly for navigation and monitoring the vehicle’s position. In a sat nav it shows the route, and in a tracker it helps establish where the car is. Transport companies also use GPS for fleet management, journey analysis and logistics planning.
GPS calculates a device’s position based on signals from at least several satellites.
GPS is a satellite positioning system that helps determine a device’s location, plot a route and provide the exact time.
A phone uses GPS, but it usually also combines data from Wi-Fi, the mobile network and sensors to determine its location faster and more accurately.
GPS accuracy is affected by tall buildings, dense forest, tunnels, the weather, receiver quality and signal strength, among other things.
Yes, GPS itself can work without the internet, but to display maps, route history and transmit the location, the app often needs a network connection.
