Donald Allwright wrote:
(1) Can you think of any depressions in Britain? I.e. places where the contour lines on
the map would wind the "wrong way"? I ask because I recently noticed that the
OS OpenData contour data is wrong around Princes Street Gardens in Edinburgh. It looks
as if the contour lines are in the right places but their heights have been mis-labelled,
as if the height labels had been added automatically by an algorithm that didn't expect
depressions. The gridded data is consistent with the incorrect labelling, probably
confirming that the gridded data is derived from the contours, rather than vice-versa.
The only other depressions that I can think of are the sunken areas in the Fens. Any
other suggestions?
There are many depressions on a small scale in carboniferous limestone areas,
where rivers/streams have disappeared underground or where caves have
collapsed. I can think of a number but whether there are any that are large
enough to show up in OS data is another question.
Yes; I am an occasional caver, as it happens. There are a few places
where my 1:25,000 OS maps show a depression contour around a cave
entrance, including Gaping Ghyll, Stream Passage Pot and Hunt Pot in
Yorkshire, and Porth Yr Ogof in Wales. But none of those show up on
1:50,000 OS maps or in the OpenData contours.
One interesting spot is where Manchester Airport runway was extended
over the Bollin Valley. The river now flows under the runway in a
culvert, making the upstream valley a depression as far as Styal.
Unfortunately, the runway was built after the OS OpenData contours were
frozen. But maybe there are some other places like this?
Any other examples?
Thanks, Phil.
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