A simple map of an urban area.
GPS, or Global Positioning System, is one of the most used technologies for tracking the location of a device. It may seem like magic, but it’s actually just cool technology and science. So, in this article, we will talk about how GPS actually tracks your position.
The GPS consists of a network of satellites orbiting Earth; there are about 30 satellites, and they are constantly in motion so that at least four of them are covering any given point on Earth. These satellites continually send signals, and your GPS device—whether it is part of your phone, part of your car, or part of a standalone unit—detects those signals.
Once your device gets these signals, it does a few things. First, it works out how far away each satellite is. Since the signal from each satellite takes a specific amount of time to get to your device and the speed of light is a known fact, the distance between the satellite and your device can easily be calculated through the equation speed = distance x time. This whole process is known as ranging.
Consider each satellite as a point on a map, emitting a signal and making a sphere around itself where your device could be. When there are signals from at least three satellites, your device is able to determine where the spheres of these three satellites intersect. This point of intersection is your exact location. With four or more satellites, it gets even better, and your device can also take into consideration the time on more satellites' clocks.
But there's more to all of this than just where these spheres meet. These signals can be fairly weak, especially when indoors or in densely packed urban spaces with high buildings that block or disrupt the signal. To handle this, your GPS device uses something called differential GPS or DGPS. Here, people/computers on ground stations, who already know their precise location, compare the signals they get to what they should be getting. They, in turn, broadcast corrections to GPS devices in their vicinity, therefore improving accuracy.
Your GPS device also works with the clocks of satellites, as mentioned before. These satellites have atomic clocks, which are super accurate, while your device does not. So, your device takes the time from several satellites, synchronizes with them, and then calculates the distances properly. Once your device knows where you are, it can do more than just show that to you on a map. If you're moving, like in a car, it can calculate your speed and direction by taking multiple position readings over time.
To keep all of this information useful, GPS systems must update the data they present because maps often change due to the building and destruction of roads, landmarks, and more. Your device may also use something called Assisted GPS or A-GPS, in which it gets help from your phone's data connection, through cell phone towers, to capture more accurate information on your location and surroundings.
Accuracy in GPS can vary. In open spaces, you might get accuracy down to a few feet, or even less, with modern technology like WAAS (Wide Area Augmentation System), which adds more corrections to the GPS signal. But in cities, under dense canopies, or inside buildings, accuracy can drop significantly.
That is how GPS works in a nutshell. It's really just a mix of satellite signals, some neat math, and a bit of help from the ground to nail down exactly where you are on Earth. Each step follows an important sequence, from the broadcasting of signals by the satellites and the interpretation of them by your device to the little blue dot on your map showing where you are.