How Does GPS Work?

Gps Featured

People use GPS extensively every day, but not many people know how it actually works. How can a smartphone know where you are, to the point you can use it as accurate directions while you drive?

Let’s open the hood on GPS and see how it works.

How GPS Finds You

Let’s say you’re hiking in the woods when you get lost. That’s alright, though: you had the smarts to download the official app for these woods. The app claims to help you find your way, no matter where you are.

The way the app does this is via five beacons set up around the forest: one in each corner and one right in the middle. You use the app to ping one of the beacons, and it tells you how far away from it you are. Easy!

Gps Towers 1

You ping tower 3, the middle one. The result comes in – you’re around 5.5 miles from the beacon. You think you’re home free, but there’s a problem: it doesn’t state which direction you are from the beacon. You could be north, south, east, or west of the beacon – there’s no knowing. As such, you can say you’re somewhere in a 5.5-mile radius around the beacon. Not very useful!

Gps Towers 2

You decide to ping tower 2 in the hopes that it’ll prove more fruitful. Not at all, as it just says you’re 3.2 miles away. No direction either. Great. This, too, is just a useless circle.

Gps Towers 3

But hold on a moment; what if we combined the data we got from beacon 3 with the one from beacon 2? If we’re 5.5 miles away from beacon 3, and 3.2 miles away from 2, then it puts us around here:

Gps Towers 4

That’s much more useful! While the information from a single beacon isn’t very useful, we get more and more of an idea of where we are when we ping multiple beacons. We can then collect the data from each beacon and find where we are.

How GPS Triangulation Works

As you may have guessed, the above example is how GPS finds you. When you enable GPS, your phone begins communicating with the GPS satellites orbiting Earth. The satellites can’t tell you where exactly you are, but it can look at how long it takes to receive the request and calculates your position based on this.

Like the above example, a single satellite will give you a rough idea of where you are. Have you ever activated GPS on a map, and all you see is a huge circle around where you currently are? That’s because your phone is talking to only one satellite, which is making a rough guess of where you are.

Things get more refined when more satellites give their responses. Your phone then takes all the information coming in from these satellites and finds where the rings meet. This is called “triangulation” and is how GPS works!

Finding Your Way with GPS

We use GPS often when finding our way, but it’s not immediately obvious how it works. Now you know how satellites locate where you are and why it sometimes puts a very useless “you are here” circle over an entire city!

Has GPS been an accurate pathfinder for you? Let us know below.

4 comments

  1. You didn’t explain how A-GPS works on a phone, which is very different than listening to satellites. Also, with 2 beacons, you’re at either of 2 points where the circles intersect.

  2. The analogy is helpful, but one big difference is that the GPS receiver never requests anything. It just listens to broadcasts. Each satellite sends a continuous stream of data. The most important bits of that are its current location and what time it is, according to its own atomic clock.
    The receiver listens for these. If it can pick up one, it at least knows what time it is fairly accurately. It doesn’t know how long the signal took to get to it though, so it can’t know exactly what time it is.
    Then it calculates its position by knowing how long each signal took to get to it by subtracting the transmitted time from its own clock. As it receives more data from more different satellites, it can calculate the “real” time more precisely, and thereby calculate its distance from each transmitter more precisely.
    Once it gets signals from three, it can unambiguously calculate its location. The circle shows the potential error based on how precise its own clock is.

  3. Doesn’t a smartphone also have a satellite GPS receiver built-in?

  4. I am a Surveyor and know all the intricacies of GPS, A-GPS, Kalman Filter that makes GPS possible, etc.
    (Even to cm and mm accuracy for us).

    But this is about the best SIMPLE explanation of GPS I have ever seen!

    Thank you for making education accessible to so many readers.

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