Tuesday, December 20, 2011

How accurate is your GPS?

I was irritated by this article in the NY Times yesterday attacking the accuracy of GPS watches and felt compelled to respond. The reporter apparently believes that Google Maps is the final arbiter of accuracy in measuring distances.

Out of curiosity I compared the distances recorded by my Garmin Forerunner 205 to the certified distances in races I have run this year to test its accuracy.  Here are the results:

(I did exclude one race.  My Garmin measured the Bridge of Lions 5k at 3.0 miles, the one and only time I measured a race shorter than the certified distance. However I received an error during that race caused by exceeding the memory capacity of the watch.  I had never cleared the history, something I routinely do now.)

That’s 99% accuracy in a consumer grade device that cost me $100 and that doesn’t even account for the fact that race directors intentionally lay out race courses a little long to account for potential error.   Nor does it account for the fact that unless you run the course perfectly, rounding turns on the tangents, you will add a few feet of distance with every turn compared to the certified route.  I think that’s pretty impressive.

Based on the simultaneous distance alerts I hear when I run with large groups, I can also confirm that this accuracy is not unique to my watch.

It’s a sad state for modern journalism that reporters routinely rely on Google for research and not much else.


  1. What are you reading that communist rag for anyway... :-P

  2. LOL. Too true. Blame Brad. I think he posts links to those articles just to get my goat.