Does the Ordnance Survey ever revise the contour lines on its
1:50,000 or 1:25,000 maps. In the South - East of England, where the
land is sinking relative to sea level by about 50cm a century, these
contour lines would over a hundred years or so be subject to
noticeable lateral "migration". For example, take the 10 metre
contour, in an area where the gradient of the slope is 1 in 200. Over
100 years this contour would migrate uphill by 100 metres, which is
2mm on the 1:50,000 map and 4mm on the 1:25,000 maps. In a few
hundred years time our contours could be out by a metre or two
vertically, and hundreds of metres horizontally. Will the O/S
respond?
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