At the end of each walk the participants often circle and discuss how far their device/software recorded the distance walked. No two are ever the same but most are usually within a 1 km spread but some outliers are sometimes considerably different. With the help of Garmin’s Basecamp software, traces and deep analysis of the .kml or.gpx files recorded by various devices and software can be studied. To this end, I have on my smartphone, 3 different recording apps, Avenza, Strava and Alltrails (apologies to the Memory-Map users). To put ‘how far did we walk?’ to the test, I went on a 15km (+ or -) walk with Avenza and Strava both recording the journey on the same Samsung Android smartphone. I assume by doing this that the location signal is the same for both apps. As was expected, the distance travelled was different. The table below shows the variation.

The superimposed traces, on Basecamp, of both apps were remarkably similar except for a 10-minute stop in suburbia to wait for another walk member whereby little real distance was covered but both apps exhibited dissimilar ‘chatter’ on their traces. Strangely enough, during a much longer stop for lunch, at a high point trig station in the bush, both traces showed a tight cluster of chatter. I have noticed, both on my own GPS and another trace, derived from Memory-Maps that large distances can appear to be travelled due to ‘zig zagging’ caused by poor true location sensing by the device or software. This usually happens in cliff lined valleys where a fix on the true location becomes uncertain. This can become magnified further if the software is on a short cycle time. In the above table you can see that Strava had far more data points than Avenza which may mean that less walk corners were cut but the traces on Basecamp do not appear to support this theory.

In conclusion, at the end of your walk when you confer with each other on ‘how far did we walk?’, agree to disagree because the correct answer is probably on the chocolate wheel.

Greg Smith