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OS map 5m contours

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Old May 6th 09, 11:29 AM posted to uk.rec.walking
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Default OS map 5m contours

"Peter Clinch" wrote in message
Roger wrote:

AFAIK all the First Series 1:25,000 contours were at 25 foot intervals
which don't translate easily into multiples of 5 metres so the OS saw an
opportunity to cut costs by dispensing with 5 metre contours on steep

"Extra detail" is not always a good thing. There's already no shortage
of mapping areas where the 10m interval is really too small to get
enough clarity and even without all the symbols obfuscating things
there's just too much brown in some places.

Norwegian highland areas are mapped with a 20m contour interval and
though it takes a bit of getting used to it actually does make a lot of
sense in places with a lot of relief. Harveys use a 15m interval which
IMHO works rather better than 10m in quite a few places in Scotland.

A 5m interval at 1:25k is not effectively much different from 10m at
1:50k. There's no problem finding instances in the Highlands on
Landrangers where contours are missed out because of lack of space,
giving a false impression of the steepness of the land.

Orienteering maps usually use 5m contours, and are most usually 1:10K,
sometimes even larger scale (1:3k the most extreme I've used). They
sometimes use intermediate contours shown as dashed "form lines" where
topographic detail is clearly visible on the ground that would be
swallowed up by conventional contouring. I think the "form line" system
is a good one as it's optional and only used by discretion where it
helps. A standardised contouring system used for both the Fens and the
Cuillin ridge, OTOH, does run into problems that what's good for one
place may not work in the other.

Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net http://www.dundee.ac.uk/~pjclinch/

Last year I was on Beinn Achaladair using my old Outdoor Leisure 25k map
there was far too much detail on it. When I got back home and looked at the
50k it was far clearer - if you get the gist.

You've come up with a good point about the Fens and Cuillin using the same
standard contours.



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