GPS Pinpoints Your Location Using Signals from Space
Getting directions on Google Maps, walking around in Pokemon GO, adding a location tag to your Instagram post - all of these rely on GPS. GPS (Global Positioning System) is a technology that uses signals from satellites orbiting about 20,000 km above Earth to figure out exactly where you are.
GPS was originally built by the U.S. military, but it was opened up for everyone to use in 1983. Today, 31 GPS satellites circle the Earth, and anyone in the world can use the system for free.
How GPS Works - Three Satellites Tell You Where You Are
The basic idea behind GPS is surprisingly simple.
- Each GPS satellite broadcasts a signal that says "here's the current time" and "here's my position"
- Your phone picks up signals from several satellites at once
- By measuring how long each signal took to arrive, your phone calculates the distance to each satellite
- With distances from three or more satellites, it uses a method called trilateration to pinpoint your location
In practice, your phone uses at least four satellites. The fourth one helps correct tiny timing errors. GPS satellites carry atomic clocks because even a one-second error would throw your position off by 300 meters. That's why accurate timekeeping is so important.
GPS Accuracy - How Precise Is It?
| Environment | Accuracy |
|---|---|
| Outdoors (open sky) | About 3 to 5 meters |
| Urban areas (between buildings) | About 10 to 30 meters (signals bounce off buildings) |
| Indoors | Mostly unusable (satellite signals can't reach inside) |
| A-GPS (Wi-Fi and cell towers combined) | About 1 to 3 meters |
Your phone doesn't rely on GPS alone. It also uses Wi-Fi access points and cell tower locations to narrow down your position. This is called A-GPS (Assisted GPS). Learn more in our article on how the internet knows your location.
Satellite Navigation Systems Around the World
GPS is the American system, but other countries have built their own satellite navigation systems too.
| System | Country | Satellites |
|---|---|---|
| GPS | United States | 31 |
| GLONASS | Russia | 24 |
| Galileo | EU | 30 |
| BeiDou | China | 35 |
| QZSS (Michibiki) | Japan | 4 |
Modern smartphones use multiple systems at the same time to get an even more accurate fix on your position.
GPS and Your Privacy
GPS is incredibly useful, but location data is one of the most sensitive types of personal information.
- Photo location data: Photos taken on your phone can have GPS coordinates embedded in them. Posting those photos on social media could reveal where you live
- App location permissions: A map app needs your location, but a game or social media app probably doesn't. Set those to "only while using" to stay safe
- Location history: Google Maps Timeline records everywhere you've been. If you don't need it, you can turn it off in your settings
Check your smartphone privacy settings and review which apps have access to your location.
Surprising Ways GPS Is Used
- Farming: Self-driving tractors use GPS to plow fields with centimeter-level precision
- Earthquake monitoring: GPS detects tiny ground movements that can signal an approaching earthquake
- Sports: Running watches use GPS to accurately track your distance and pace
- Time synchronization: Banks and cell towers rely on GPS atomic clocks to keep their systems perfectly in sync
Want to dig deeper into how GPS works? Books about GPS technology are a great resource. You can also visit IP Checker to see how your approximate location can be estimated from your IP address alone.