Jason, Yes, I'll try to do this over the weekend. Give me an off-line
poke if I forget.
Mike
At 14:45 09/03/2011, Jason Cunningham wrote:
Hi Mike,
Can you provide us with a grid ref(s) for a location where the OS
data is wrong
Jason
On 9 March 2011 13:33, Michael Collinson
<<mailto:m...@ayeltd.biz>m...@ayeltd.biz> wrote:
At 13:29 09/03/2011, Chris Hill wrote:
On 09/03/11 11:57, Michael Collinson wrote:
At 12:32 10/02/2011, Andy Robinson (blackadder-lists) wrote:
Henry Gomersall [mailto:h...@cantab.net] wrote:
>Sent: 10 February 2011 11:07 AM
>To: Peter Miller
>Cc: Talk GB
>Subject: Re: [Talk-GB] Incorrect use of OS VectorMap District when mapping?
>
>On Thu, 2011-02-10 at 10:30 +0000, Peter Miller wrote:
>> On reflection possibly we should use river-bank as that has more
>> information in it, but recommend that anyone importing does a 'bridge
>> cleanup' at the same time.
>
>This is an area I'm actually really interested in (for rural rivers) and
keen to
>contribute. So far I've been put off by exactly this problem. Is a
reasonable
>approach to use the OS data for river edges and then fill in the gaps
(bridges
>etc) with OSM data?
+1
If the OS vector data is only assumed to be the banks and the additional
data for flow direction, bridges and other features are added from
survey/BING etc then we should end up with a very functional dataset.
A late response to this thread, but a word of caution. Comparing
Bing imagery recently for several Yorkshire rivers with folk's
riverbanks derived from OS data indicates that very frequently the
OS are not tracing the riverbank as the dividing line between water
(clear river channel) and land (grass, scrub) but the top of the
riverbank or where the rough "verge" meets pasture land.
A further word of caution: Bing and all other imagery only shows a
snapshot of the way things are, often many years ago, and in an
indeterminate state of water level. Some rivers have tidal
influences, some rivers have very different levels in flood or
drought. Sometimes where the rough "verge" meets pasture land is the
highest point the water reaches regularly, but still only occasionally.
Certainly both Chris' and Phillip's cautions are certainly true but
I've paid particular attention to the River Wharfe mid-reaches,
which I know very well and flows in a well-defined channel with high
banks and has not shifted markedly in the last 40 years. In places,
it is almost twice as wide as it should be. Chris may be right in
suggesting that the highest water mark is being mapped, but why map
the 10 - 25-year flood event level rather than the natural bank
line? I am tempted to think that automated software has been used
which like PGS coastlines occasionally gets confused by nearby
lineaments. I also recall comparing with digitised 25:000 maps
(vintage 1900 - 1960 surveying) and noticing that it correlates much
more closely with Bing than StreetView. Needs more analysis but be aware!
Mike
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