Updated heights

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By TallPaul on 23/08/18 at 7:50am

We've been working behind the scenes on updating our height data which we use in our GPS mapping application and also for our walks. This has involved merging NASA height data for Ireland and the Isle of Man with OS Terrain 50 data for Great Britain (previously we were using NASA height data for Ireland and an older version of the OS's height data for Great Britain and Isle of Man).

The consequence of this is that if you query the height of a particular point you may find that it has changed slightly.

This is largely not because land has really changed in height but because OS, in their infinite wisdom, have changed the 50m x 50m height grid they provide us with. It was previously given to us at easting and northings ending 00 or 50 and we estimated the heights at other locations from that. It's now coordinates ending 25 and 75 so with slightly different heights each time. Again we're estimating heights for other locations but as the underlying data has changed so have the results.

They're also now giving us heights to the nearest 10cm rather than the nearest metre.

However the differences are small, in the order of 10m maximum and typically more like 1m or 2m, and the overall effect on profiles, and total ascent and descent seem to be negligible - certainly in all the test cases we're tried - so you shouldn't notice any significant differences if you look back on past tracks or routes (and if you do see a difference the new figures are likely to be more accurate).

As a result of this exercise, and one the main reasons we did it, is improved relief shading on our WayMaps tiles (including north Shetland for the first time). We're still processing that now but we'll let you know, either here or on the blog, when that's live.

By TallPaul on 27/08/18 at 4:45pm

The new tiles are now live, and here's Shetland before:

And after:

Now with everything north of 60° North showing relief shading.

As usual this release also includes the latest updates from our data sources, especially OpenStreetMap.

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