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Old May 6th 09, 07:54 AM posted to uk.rec.walking
Tom Crispin
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Posts: 318
Default OS map 5m contours

On Wed, 06 May 2009 02:28:37 +0100, Chris Street
wrote:

Tom Crispin wrote:
On Tue, 5 May 2009 21:21:53 +0100, "Mike Mason"
wrote:

Just been setting up a walk near New Radnor for tomorrow and noticed that in
the area contour lines seem to be in 5 metre intervals rather than 10 metre
intervals. I've never seen this before on an OS map. Does anyone know of
other areas where the contours are mapped at 5 metre intervals and is there
any particular reason for this.


I have about 90 Explorer maps covering most hill regions of the United
Kingdom, other than N. Ireland. I wondered for a while if the maximum
height of the land on the map may be the factor by which OS chooses to
use 5m or 10m contour intervals. However, Explorer 109 goes up to
420m and has contours at 10m intervals; Explorer 201 rises to 610m and
has 5m contours. So that theory is shot to pieces.


But how low does Explorer 201 fall? Perhaps it's to do with total range
on a map not max altitude?


119m on the River Lugg was the lowest spot height, and below the 120
contour on both the Rivers Clun and Teme are the lowest points: that
gives the map a range of 491m or less. Explorer 109 falls to the
Atlantic Ocean giving that map a full range of 420m. So that's
another fine theory shot to pieces.