More on Mapping
The big problem seems to be with roads, tracks and paths. Any road on the map is merely a graphic, scaling at maybe 30 m wide on a 1:50,000, and, crucially, unconnected to the height data. This is why, on Memory Map, the occupants of the cottage near Braemar at NO127909 are apparently faced with the problem of the opposite side of the road being 16 metres (52 ft) higher than it is outside the house (must be a right bugger backing the car out of the garage!).
Thus any route plotted along this road, if it deviates slightly from one side to the other, will record 16 metres of additional ascent at this point alone - and along its length these errors will add up to a great deal.
Zoom in on Memory Map and pick any land rover track contouring around a hill, between contours. Using a paper map, we will say that the ascent here is zero, and so it is. But check the height on the left and right hand sides of the track, and you will find that it often apparently slopes by as much as 3m or 4m. The same applies to canals - sloping water!
When we plot a route we might stay within the confines of a road or track, but it is simply not possible to get an accurate ascent figure whilst the software is incapable of recognising that a track or road is (mostly) flat from side to side.
That said, our 'paper' method does not take account of undulations along the track that do not break the contour line. However, I reckon that any underestimation that this might produce is relatively insignificant.
One for the boffins to work on, but for now ..... count those contours!!!
I'll go back to sleep now.
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