How accurate is Map my Run?

I’ve been relying on ‘Map my Run’ to track my runs over the last month or so, since my beloved Garmin Forerunner 110 gave up the ghost, thanks to my accidentally leaving it in my shorts and then washing them.

I loved that Garmin… even if it was the cheap version, even thought it was 6 years old, even though the strap had disintegrated, meaning I had to store it in a running bag…. It did the job!

More importantly, I felt reasonably secure in the knowledge that Garmins are the most accurate geo-tracking devices around, given that they receive their geo-data directly from satellites (which explains why they sometimes take a little while to find them).

We had some good times together, all lovingly recorded on Garmin Connect, up until December 2017 at least.

But that was then, and this is now, and with the Forerunner ‘washed out’ (excuse the most excellent pun, and also see the **edit below**) and me being a tight wad, I’ve gone through a phase of ‘no tracking’ (maybe more on that later), and now to ‘cheap tracking’, and ‘Map my Run’ is free, so as cheap as it gets, assuming you’ve already got a smart phone of course.

However, I’m not convinced that it’s as accurate as my Garmin. It failed to record a couple of ‘tight circles’ I incorporated into my one of my runs last week, and after a bit of digging I’ve discovered why phone trackers.

It’s got nothing to do with the app, it’s got to do with difference between the way the geo-sensors in my phone gather data compared to how my Garmin (used to) measure data.

Why mobile phone geo-tracking apps aren’t (generally*) as accurate as Garmins….

The app running in your phone is entirely dependent on your phone’s GPS sensor.

A smartphone’s GPS censor receives location data from cell phone towers or Wi-Fi hotspots;  Garmins receive their location data directly from satellites.

This means that while your Garmin will receive continuous geo-location data, your phone (and the tracking app it’s running) will only receive periodic geo-data from the fixed positions of the towers and hotspots.

This fixed position data is then relayed to your phone, and averaged out, which explains the inaccuracy compared to the more direct-data feed with the Garmin.

You can see the difference in the way the two devices record your pace….

The pace charts below are from a similar route, with ‘kissing gates’ where I have to drastically slow down for a few seconds as I approach and even come to a dead halt….. the Garmin’s tracking immediately below shows you the ‘dead halts’…. The gaps are basically where the kissing gates are on the route.

In contrast Map My Run’s tracking (below) shows no ‘dead stops’, even though I did come to some ‘dead stops’, because it is averaging out data from fixed positions. Hence it is simply inaccurate.

(*I say ‘generally’ because there may be some ‘direct to satellite phones out there)

So how inaccurate is Map my Run compared to the Garmin….?

**Oh the marvels of Garmin… having written above that my Forerunner was knackered, I’ve just found that it’s not… on the off chance I decided to give it a charge and it’s working so I did a little 600 meter walking experiment to compare Map My Run directly to the Garmin’s tracking….


Phone/ GPS tracker (Map my Run) 





As you can see, in just 600 meters, Map my Run overestimates by 0.01 meter, so let’s say this is 0.02 for a Kilometer, and .20 meters over a 10 K run.

Now if that’s under race conditions, 20 extra meters at the end of a race that you might not have expected is certainly enough to mean you miss out on a PB.

What factors affect THE accuracy OF YER GPS TRACKER?

According to this article, there seem to be three main ones:

  1. how close you are to the ‘fixed’ geo-locations, and how many of them there are…. I guess that being out in the country may not be as accurate as being in a city, although point 2 might negate this…
  2. Buildings, trees  and alien spacecraft can obscure your GPS connection and so make readings less accurate, so if you want better accuracy, avoid aliens.
  3. Making tight turns will affect the accuracy of your phones GPS data….. the reading will be more accurate if you run 10 miles in large circle or a straight line, rather than running 10 miles back and forward along a 100 meter track.

Final thoughts…does accuracy matter that much?

Having done this little experiment I’m glad my Garmin’s working again TBH. HOWEVER, at least I now know the degree of inaccuracy of Map My Run, so I can simply adjust accordingly.

If I had to rely on Map my Run, I guess it wouldn’t matter for me as I;m not planning on racing any time soon, but I wouldn’t want to use it if I was racing, given the misleading data.

I’m going to assume that at least I get a reliable measurement, if not a valid measurement of my runs, so even if it is inaccurate, it has the same degree of inaccuracy every run, so I can still use it to track progress. Having said that, this may not be the case if continual improvements are being made?!?


107 thoughts on “How accurate is Map my Run?”

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