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Written on 01/02/17 by Paul Oldham

On Tracks and Routes

People who buy the GPX routes of our walks are sometimes confused that the route appears to be shorter than the walk. To illustrate here's an example of an email we received today about our walk Nab Scar and Alcock Tarn. It said:

I purchased the GPX for this route. The website says it is 5 miles but the GPX is only a 5km (3 mile) route.

Please can you look into this?

There's actually two issues in play here. The first is that we've found that different GPX software often gives different results for the length of a GPX track or route. So if you take this route file and feed it into our GPX mapping application it says the route is 5.90km, not 5km. These sort of differences are not unusual - even if the user (or their application) isn't rounding down.

Walk 74, step 6 map But the more fundamental issue, and why this GPX file is always going to be shorter than the walk length is because it is a GPX route, so that's a set of waypoints which you walk from one to the next to complete the walk.

Each waypoint is some distance from the previous one. That's normal, you don't want too many waypoints on a route: they're there to guide you forwards not log every minor twist and turn.

However when we work out the walk distance we rely on the GPX track we recorded with our GPS while walking the route. That accurately records where we walked as it logs many more points. The consequence of this is that a track accurately reports distance whereas a route is always going to be shorter as it (quite literally) cuts corners.

This is illustrated very nicely by step 6 of the walk. If you look at the little map for that step (shown here on the right), which is displaying the GPX track for that section i.e. where we actually walked, it shows that we had to zig zag down the hill.

The path down is obvious so if you were to look at the route GPX you will find that we've put a waypoint at the top and another at the bottom, hence it looks like a line straight down and is a lot shorter, at least 50% if not more.

This will happen, although not to such an extreme extent, as you walk between any two route waypoints as your path is pretty much never a dead straight line. As a result the route will always be shorter than the track.

Anyway, the bottom line is: rely on our walk instructions for distance and the route GPX for waypoint to waypoint directions.

Tagged: GPS, maps, walks

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