How GPS Really Works—and Why It Sometimes Gets You Lost
On a recent trip to Grand Teton National Park in Wyoming, we followed a road around the back side of the Elk Refuge just south of the park (it’s open to the public). At the head of one private driveway, we saw a sign that read, “Your GPS is wrong—this isn’t the place you’re looking for; keep going down the road.” My husband and I laughed later about how many times GPS directions led us slightly — or not so slightly — astray.
I’ve read and heard many anecdotes of navigation sending drivers to the wrong entrance (or the wrong business entirely), photos tagged with a slightly incorrect location, and fitness trackers miscalculating distance. In the early days of iPhone fitness trackers, I watched an app track me all over a twelve-block square while walking one block. As a tech professional, I realize that while GPS feels instant and precise, it’s more complex than it looks.
That’s why I thought that GPS would make a good topic for a post. I wanted to dig into what GPS actually is, how it finds your location, the role of timing, common causes of errors, and some improvements on the horizon. Shall we get started?
What GPS Actually Is (in Plain English)
GPS is the acronym for Global Positioning System, a U.S. satellite-based navigation system made up of a network of satellites orbiting the Earth and the ground control stations that manage them. GPS was developed for military use, but it’s used now in all kinds of everyday devices. It’s an amazing piece of technology that can work in most places on Earth. I say “most” because it has a big limitation: it needs a reasonably clear view of the sky. That may not sound like a harsh constraint, but it mattered a lot to me when I made a wrong turn into a densely forested area and had to guess my way out because my GPS receiver couldn’t get a solid lock on enough satellites.
We often say “my GPS” when we’re talking about finding our way with a phone or a dedicated navigation device. If we want to be clear and accurate, though, we’re really talking about two separate pieces. Strictly speaking, “GPS” is the system of satellites and the ground control network that monitors them, updates their clocks and orbits, and broadcasts timing and positioning signals. The part we use is a GPS receiver that listens for those signals and turns them into a location on a map.
How GPS Finds Your Location
Accurate geolocation requires signals from at least four satellites. On a recent trip to Grand Teton National Park in Wyoming, we followed a road around the back side of the Elk Refuge just south of the park (it’s open to the public). At the head of one private driveway, we saw a sign that basically said, “Your GPS is wrong—this isn’t the place you’re looking for; keep going down the road.” My husband and I laughed later about how many times GPS directions led us slightly — or not so slightly — astray. I’ve read and heard many anecdotes of navigation sending drivers to the wrong entrance (or the wrong business entirely), photos tagged with a slightly incorrect location, and fitness trackers miscalculating distance.
We often say “my GPS” when we’re talking about finding our way with a phone or a dedicated navigation device. If we want to be clear and accurate, though, we’re really talking about two separate pieces. Strictly speaking, “GPS” is the system of satellites and the ground control network that monitors them, updates their clocks and orbits, and broadcasts timing and positioning signals. The part we use is a GPS receiver that listens for those signals and turns them into a location on a map.
The Role of Timing: Why Atomic Clocks Matter
In the ”What GPS Actually Is” section, I mentioned clocks. Clocks are critical to GPS accuracy, to the extent that the system requires extremely precise timing. Even tiny timing errors can cause large location errors. For that reason, satellites use atomic clocks, and your phone only approximates the timing. Your phone gets its time from cell towers, which in turn get their time from GPS satellites and other sources.
Instead of relying on a swinging pendulum, an escapement wheel, or a vibrating quartz crystal, an atomic clock uses the ultra-steady “oscillation” of atoms jumping between two specific energy levels as its time reference. Onboard solar panels and batteries provide power for the satellite’s electronics, including its clocks. Careful monitoring from the ground keeps their behavior predictable and correctable over very long time periods.
Each GPS satellite is a flying radio beacon, constantly broadcasting a precisely time-stamped signal. The signal includes that satellite’s identifier, its orbital information (so your device can figure out where it is), and a very precise timestamp from its atomic clock. Your receiver listens for several satellite signals at once, recognizes their unique patterns in radio noise, and uses the tiny difference between when the satellite sent the signal and when it arrived to figure out where it must be. That’s why atomic clocks matter.
Common Causes of GPS Errors
GPS and satellite-based technology work great — until it doesn’t. Most often, the “not working” condition is temporary – momentary, even. Persistent errors and issues, though, can usually be narrowed down to a few common causes.
What’s blocking the signal?
The first thing to look for is obstructions — like the deep woods I mentioned earlier. It doesn’t have to be woods, though. Standing in an “urban canyon,” between two rows of very tall buildings, can also interfere with satellite signals. The signals can be blocked, yes, but also reflected off the surfaces of the buildings or other structures. Signals that bounce off surfaces before reaching your device create inaccurate distance calculations.
The sky itself
Then there are things in the atmosphere — specifically, the ionosphere and troposphere — that can create interference. High up, the ionosphere is full of charged particles that slow GPS signals in a way that depends on their frequency and on space weather. Down where our weather lives, the troposphere bends and slows the signals depending on air density and water vapor. Neither one usually knocks GPS out completely, but both can stretch the signal’s travel time just enough to nudge your location a few meters off.
Configuration
The geometry of the satellite network itself is also a factor. Satellites work best when they’re pretty well spread out in the sky. Poor geometry — for example, when the satellites you can see are all clustered in one part of the sky — can reduce accuracy.
People and their things
Then there are the device and human issues. It’s just a reality that your phone is not equal to a dedicated high-end GPS unit. Antenna quality and battery-saving modes both play a part in that disparity. The antennas in our phones are “good enough” for our call quality (most of the time) and “good enough” for most GPS activities. And if you’ve ever used your GPS on your phone for several hours, you can appreciate that battery-saving mode — but it carries a performance cost.
Assisted GPS (A-GPS) and Modern Enhancements
The GPS that most of us use is on our cell phones. It’s not really “pure” GPS because it uses cellular and Wi-Fi data to speed up location fixes. That also improves performance in cities and inside buildings (always assuming you can get a signal in the building). However, it also imposes its own set of limitations.
For example, on each trip we’ve made to Yellowstone and through much of the Great Smoky Mountains National Park, the GPS part could keep tracking our location. Once we drove beyond the cached map tiles on the phone, though, the app didn’t have images to draw underneath the blue dot that represents our location. The GPS was working fine; the problem was that the map app couldn’t download fresh tiles without a data connection.
I’ve since found out that both Google Maps and Apple Maps will let you download areas ahead of time so that you can navigate without cell service. You just have to get it set up while you still have a data connection. Here’s the link to the instructions for Google Maps. This is the link to the instructions for Apple Maps.
Additionally, modern receivers don’t just use GPS—they use multiple Global Navigation Satellite Systems (GNSS) constellations. For example, GPS is just the original U.S. satellite navigation system. We also have GLONASS in Russia, Galileo in Europe, and BeiDou in China. More constellations = more satellites in view, which usually means a quicker, more accurate, and more reliable location.
How to Improve GPS Accuracy – Some Practical Tips
If you’re looking at your phone and it’s showing you in a different location, even just a block or two, here are a few things that can help:
- Move to an open area with a clear view of the sky
- Turn location services off and back on
- Calibrate your compass
- Keep device software updated
- Wait a few seconds for signal lock
Still, GPS is typically accurate within a few meters — that’s somewhere between 5 and 15 feet — under good conditions. Given the great distances involved, that’s pretty amazing.
Your Turn
I’d love to hear your GPS oopsies. I often have to tell my husband, “Hang on a second, I need to let the signal catch up with us.” Where has it steered you wrong? Several missed turns in one city? Drop your story into the comments!
ten have to tell my husband, “Hang on a second, I need to let the signal catch up with us.” Where has it steered you wrong? Several missed turns in one city? Drop your story into the comments!
My photography shops are https://www.oakwoodfineartphotography.com/ and https://oakwoodfineart.etsy.com, my merch shop is https://www.zazzle.com/store/south_fried_shop.
Check out my New and Featured page – the latest photos and merch I’ve added to my shops! https://oakwoodexperience.com/new-and-featured/
Curious about safeguarding your digital life without getting lost in the technical weeds? Check out ‘Your Data, Your Devices, and You’—a straightforward guide to understanding and protecting your online presence. Perfect for those who love tech but not the jargon. Available now on Amazon:
https://www.amazon.com/Your-Data-Devices-Easy-Follow-ebook/dp/B0D5287NR3
