OS map 5m contours
 

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.

Mike Mason

OS map 5m contours
 

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.

Mike Mason


Can you be more precise on the location please?

Gerald

OS map 5m contours
 

Gerald wrote:
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.

Mike Mason

Can you be more precise on the location please?

Gerald

Having checked my maps I see that the Explorer series 1:25,000 are as
you state at 5 m interval contours not just on map 201 for that area but
also on the others I checked. Landranger Series 1:50,000 are 10 m
intervals on map 148 for that area and a few others I checked.

Gerald

OS map 5m contours
 

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.

OS map 5m contours
 

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?

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.

OS map 5m contours
 

In article , Mike Mason
writes
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 think it is just where the sheet is generally not very hilly. In
relatively flat areas 10m contours would mean almost no contours!

When I first noticed two adjacent bits of mapping with different contour
intervals I initially thought there was a very steep sided valley
nearby. Turned out the 5m contours made it look that way until I looked
closer!

Here is that example just to the east of Black Hill in the northern Peak
District:

http://www.streetmap.co.uk/map.srf?X...4875&A=Y&Z=115

--

Dominic Sexton

OS map 5m contours
 

Tom Crispin wrote

So that's another fine theory shot to pieces.

What about density of rights of way, and thus liklihood
of access ? It's not unreasonable to make maps that are
more likely to be used in detail more detailed ?

Chris
--
Photography by Chris Gilbert
www.ravenseyegallery.co.uk
Internet life support for small businesses
www.ravenseye.plus.com
Affordable web sites
www.sitegateway.net

OS map 5m contours
 

The message
from Dominic Sexton contains these words:

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 think it is just where the sheet is generally not very hilly. In
relatively flat areas 10m contours would mean almost no contours!

When I first noticed two adjacent bits of mapping with different contour
intervals I initially thought there was a very steep sided valley
nearby. Turned out the 5m contours made it look that way until I looked
closer!

It's the OS caught on the horns of a metric dilemma.

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
ground. A pity it didn't result in more contours and less crag symbols
on the steep ground but the OS really do like filling the maps with
symbols rather than actual detail.

--
Roger Chapman
Nearest Marilyn still to be visited - Great Orme.
89 miles as the crow flies,
considerably more as the walker drives.

OS map 5m contours
 

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
ground.

"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.

Pete.
--
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/