What Is GPS

GPS (Global Positioning System) is a satellite-based positioning system operated by the United States. The umbrella term for satellite positioning as a whole is GNSS (global navigation satellite system), and GPS is one member of that family. Russia's GLONASS, the EU's Galileo, China's BeiDou, and Japan's Quasi-Zenith Satellite System (QZSS, Michibiki) also belong to GNSS, and most smartphones receive several of these constellations at once when working out where they are.

The baseline GPS arrangement is a set of 24 slots: six orbital planes around the Earth with four slots each, which is what makes at least four satellites visible from virtually anywhere on the ground. Why four? The unknowns you want are latitude, longitude, and altitude, but the measured distance to each satellite also carries the error of the receiver's own clock. That clock offset has to be solved as a fourth unknown, so four satellite signals are needed.

GPS Accuracy and Complementary Technologies

Positioning accuracy varies widely with the receiving environment. GPS.gov, the official United States government source on GPS, states that GPS-enabled smartphones are typically accurate to within a 4.9 m radius under open sky, and that their accuracy worsens near buildings, bridges, and trees. When a signal reaches the receiver after bouncing off a wall, the distance to the satellite is computed as longer than it really is, which is why in a city centre your position can jump to the other side of the street or to the next block.

Smartphones compensate for this by combining the positions of Wi-Fi access points and cell towers with the movement picked up by the accelerometer and gyroscope. Indoors, where satellite signals barely reach, Wi-Fi and Bluetooth beacon positioning are used instead.

The other piece is A-GPS (Assisted GPS). Satellites broadcast their own orbital data, but waiting for that slow signal to arrive in full delays the first fix. A-GPS delivers the same information over the mobile network or Wi-Fi ahead of time, leaving the receiver warmed up. That groundwork is why a map app can show your position moments after you open it.

Location Data and Privacy

Location data is sensitive personal information. Because patterns of movement reveal where you live and work, it is worth managing location permissions app by app.

Reserve "Always allow" for apps that genuinely need it, such as navigation
Make "While using the app" your default
On iOS 14 and later and Android 12 and later, you can choose whether an app receives your precise or approximate location; pick approximate for apps that do not need street-address precision
Strip the location data (Exif) from photos before posting them on social media

GPS vs GeoIP

GPS receives satellite signals and lets the device itself calculate the position, narrowing it down to a few metres when the sky is open. GeoIP, by contrast, estimates location at the city level from an IP address, an entirely different order of precision. The location shown on our homepage uses GeoIP and is not as precise as GPS.

To explore how the internet figures out where you are - including the differences between GPS, Wi-Fi positioning, and IP-based location - see How the Internet Knows Where You Are - IP Addresses and Location.

Common Misconceptions

GPS constantly monitors your location: A GPS receiver only listens to the signals from the satellites; it never transmits back to them. When people talk about being tracked by GPS, what actually sends the position out is an app on the device or the operating system's location sharing, not the GPS signal itself.
Turning off location services makes you untraceable: Even with GPS switched off, your approximate location can be estimated from Wi-Fi networks and cell towers. Estimation from the IP address you connect with (GeoIP) remains as a separate route.

GPS vs GeoIP Comparison

GPS

Satellite signals received and computed on the device. Narrows down to a few metres under open sky, but accuracy drops indoors and among tall buildings.

GeoIP

City-level estimation from IP addresses. Determined server-side. Inaccurate when using a VPN.

GPS