I Don’t Want to Run with GPS Anymore
By: Erik Hermansen
Tags: Gps, Running, Fitness, Jogging, Running Tips

Ah, the wondrous powers of technology!

It is absolutely incredible that your phone or the little watch on your wrist communicates with satellites orbiting the earth to determine your location on the face of the planet. I’ve been working professionally with GPS data for 12 years as a software engineer on GIS and automotive systems, and I will never be jaded about this little miracle. GPS is great!

However, as a runner, I’m ready to throw my GPS watch in the trash. Do you want it? The thing is worthless to me.

The problem is reliability. On most runs, I care about my distance travelled and want it to be accurate. It’s not helpful to learn that I probably ran 10 miles.

On some runs, the exact distance doesn’t matter because I’m just fun-running. Or my training goals on a run don’t relate to distance. For those “distance doesn’t matter” runs, a GPS device’s unreliable calculations would be acceptable, but they are also moot.

I can hear somebody objecting, “What do you mean unreliable? You should just get the GarmoMaxSportProElite watch. It never fails.”

The ultimate watch for runners is here!

Sigh. I know better.

The different GPS devices on the market perform with varying levels of accuracy. But they all have limitations from relying on the same 24 Earth-orbiting satellites, and the same laws of electromagnetism.

I will admit it’s possible that…

In the places you run, GPS signals are never blocked by obstacles like tall buildings.

Your routes never contain tight curves, which cause the typical 25-foot “give or take” of GPS measurement to under-report your distance.

Your device will switch between multiple satellite signals efficiently, and never over-represent waning signals.

The smoothing algorithm applied to points in your run by the device will always make correct guesses about where you are, and not get confused by big changes to your pace.

The government will never set a satellite to a “selective availability” mode that intentionally reduces accuracy (yes, this one is a little bit “tinfoil hat”).

You always remember to charge the battery fully on your device.

All these things are possible. But unlikely.

Sorry for the nerd talk — I’m just trying to give you a sense of why it’s hard for a phone or watch to track your position accurately in all the different places and times you could go out for a run.

For me, this is not theoretical. Several times, I’ve had what I thought were terrible runs. But my perception of my own slowness was just caused by a GPS device failing to record a mile or two. I remember being demoralized by a split time of 9:58 that was actually 7:22 — the device had recorded the wrong distance, probably due to tall buildings in one part of the route.

And it’s also gone the other way. I’ve had my Magic Runs where it seemed like I’d suddenly, effortlessly chopped 30 seconds off my split time. Did I make it to the next level? Had the Gods of Greece bestowed greatness upon me?

Nope. Just a GPS glitch reporting I ran a longer distance than I actually did.

And even if it’s 9 times out of 10 that my gear accurately reports distance, that 10% chance of getting bad data puts everything in doubt.

GPS Lock

A “GPS Lock” (also called a “fix”) means the device has successfully received signals from multiple satellites (typically four) sufficient to calculate a position. The name is misleading because it implies that once you have a “lock” you won’t lose it or experience a degradation of quality in the information received. But that happens all the time.

The watches seem to do better at calculating position than the phones. I think that’s because they tend to pessimistically wait for a GPS lock before they start measuring distance. Whereas, the apps on phones that I’ve seen don’t wait for a GPS lock. Why the difference? I haven’t figured it out yet, but I suspect the answer has to do with location services available to Google and Apple that cause them to be more willing to guess location prior to GPS lock.

Some watches, (looking at you, TomTom) will not even let you start the timer until they have a GPS lock. This “wait for the lock” practice is smart, but not always welcome. I have stood around waiting for the GPS lock too many times. There is something humiliating about waiting for permission from my watch to begin a run. I don’t like it.

Sometimes, the watch gets a GPS lock, and loses it later. At the gym I go to, there is a little indoor track on the fifth floor of the building I like to use for shorter runs. My watch, even after getting a GPS lock, is extremely confused about how I am moving through space, as you can see from the image below.

How my stupid watch records me running 57 times around a small loop.

Since I’m not actually Superman flying in circles around a skyscraper, I know this recorded route is garbage. The inaccuracies can mostly be attributed to frequently losing the GPS signal as my route took me away from the exterior of the building where the signal was strong. But also the tight loop of the course isn’t well-tracked by the “give or take 25 feet” typical resolution of GPS.

So at this point, having over a decade of insight into the technical limitations of GPS, and plenty of runs where I’ve been misled by the Latest and Greatest GPS Thingy, I’m opting out of GPS for tracking runs.

Instead, I’m just doing it the old-fashioned way. I know the distance of the running route through non-GPS means, and I use a stopwatch or app with basic start/stop functions to record time. To get my split pace, divide distance by time.

It’s more work, but I don’t have to trust the whims of satellite communication to measure distance.

Calculating Route Distance without GPS

To know the distance without using a GPS device requires me to do a little homework in advance of a run.

If I’m running on a course with a commonly known distance, then sometimes it’s easy. For example, a standard running track is 400 meters per lap. But I’m cautious about accepting a posted distance for a course. I thought for a long time that the distance around Green Lake, a popular place to run in Seattle, was three miles. I thought this because I read it on an official-looking webpage somewhere.

But after measuring it myself, I now know that it’s only 2.88 miles around that lake — not three. Ouch! I did not enjoy learning that my splits were 8-something instead of 7-something. But in the end, knowing the truth is always better.

How can you measure the distance yourself? Google Maps includes a great, free tool for this. And keep in mind, that I mean calculating distance before the run — not during.

On my computer or phone, I can plot the points of the route, and use Google Map’s “measure distance” feature to see how long the route is. I take particular care to plot tightly along all the little curves and turns. After plotting out the route, I’ll save starting locations, “turn-around” points, and other waypoints as labelled favorites on the map. I only need to plot out a route like this once.

An example route plotted in Google Maps with the “Measure Distance” feature.

If you want to do the same thing, I’d give the following advice:

Physically run the route at least once to gain some familiarity with its twists and turns. It can be a lot tougher to plot the route if you’ve never seen it in-person before.

Pay attention to the minor choices you make in a route, e.g. where is the place that you like to cross that busy street? Do you take the little dirt path that runs next to the lake or stay on the main paved path? If there are a lot of choices like this to remember, come up with a general approach, e.g. “always go left”, that simplifies it. Your desired end result is just that the route you run matches the route you plot.

Set the map zoom level close enough that it allows you plot the route in sufficient detail. If you’re zoomed out too far, your measured distance will tend to be too short as it misses all the little curves that add time to your run.

There’s lots of software that lets you plot out routes like this. Google Maps works on a web page, Android, and iPhone, so pretty much anybody can use it. If you want to get deeper into maps and routes with more powerful tools, you might look into GIS software.

Just Try It Once

If all this route plotting sounds like too much work, at least try it one time on your favorite running route. See if your GPS-reported distance matches your plotted distance. You might learn you are much faster or slower than you thought.