« Data portability | Main | Now I know a little more about rake-pipeline »

Which do you believe, the map or the GPS?

If you read my last grumpiness regarding Nike+, you probably know that the answer to the above question is, “It depends.”

It turns out Strava has the same problem as Nike+ when it comes to using the GPS in the iPhone to track runs. Simply put, both apps trust that the GPS track from the phone is 100% reliable; once a run has been tracked, there is no option to correct the track or replace it with something generated from a map.

This would be wonderful if the GPS track was, in fact, 100% reliable. But for some reason in the last few weeks, my GPS tracks have been consistently bad. I’ve had seven-mile runs marked as two and a half, two-and-a-half mile runs marked as three… it goes on and on. I don’t know if the problem is the phone hardware, the apps, local topography, local weather, solar weather, or some combination, but it’s pretty consistently bad.

And it highlights the problem with using GPS tracks to get run distance (or much other run data): GPS as a technology is much more precise than it is accurate. Put another way, like email, GPS is a “best effort” technology (much like email). It can be wrong, and if it’s wrong it will not apologize nor necessarily admit the error.

So why don’t either of these logging systems accept an alternative? All they need is an option—it can be on the website, it doesn’t need to be right in the phone app—to indicate for a given run if the GPS track is actually correct. The user could have the option to upload a .gpx file with a better map track if they want to generate one with another app. (It’s hypothetically possible to use the Gmap-pedometer to create a gpx file, and use that to record a new run with Strava, but so far the gpx files I’ve tried uploading to Strava have failed.)

Introducing this option of human oversight is a simple way of accounting for GPS’s lack of accuracy. I’m sure most of the app developers want to avoid that degree of complication, but in doing so, they’re placing more trust in a fallible technology than it really deserves.

ETA: So the issue with my GPS inaccuracy turned out to be the iPhone and not the apps. Still, how do I correct the logs?

Post a comment