Hi Hillary,
You made a fascinating observation about the impact that a rise in sea
level would have on the location of contour lines portrayed on large
scaled maps. It would seem that with a rise in sea level these lines
would indeed shift noticeably over time on maps scaled at 1:50,000 or
1:25,000, particularly where the topography of the land is characterized
by gentle slopes with a mild gradient.
Unfortunately, I don't really know what the practice of the UK Ordnance
Survey is with respect to updating contour lines. I contacted the
Ordnance Survey a few days ago, and posed the question directly to them.
I am currently waiting for their response, and will gladly forward it to
you as soon as I receive it. If you wish, you can also try to contact
them by visiting their site at: "www.ordsvy.gov.uk/".
I have looked at a rather different aspect of the problem, and focused
exclusively on the impact that a rise in sea level would have on the
limits of maritime jurisdictional zones seaward of the low-water line,
as opposed to contour lines which are situated on land, or bathymetric
lines which basically portray the depth of the water column. The
problems that a rise in sea level creates for the limits of maritime
zones is somewhat different than the problems it would generate for
contour lines or bathymetric lines, and I am not sure how helpful my
comments would be.
Hopefully, the media services of the Ordnance Survey will be able to
shed some light on the question you asked.
I am very interested in learning more about your work, so feel free to
contact me, and keep in touch.
Dr. Alain K. Khadem
17 Gatelot Avenue,
Lake Ronkonkoma
NY, 11779-2304 USA
Tel: (516) 981-6808
(516) 981-6807
Fax: (516) 981-6805
Hillary Shaw asked:
>
>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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