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Jason, Yes, I'll try to do this over the weekend. Give me an off-line
poke if I forget.<br><br>
Mike<br><br>
<br>
At 14:45 09/03/2011, Jason Cunningham wrote:<br>
<blockquote type=cite class=cite cite="">Hi Mike, <br><br>
Can you provide us with a grid ref(s) for a location where the OS data is
wrong<br><br>
Jason<br><br>
On 9 March 2011 13:33, Michael Collinson
<<a href="mailto:mike@ayeltd.biz">mike@ayeltd.biz</a>> wrote:<br>
<dl>
<dd>At 13:29 09/03/2011, Chris Hill wrote:<br>
<dl>
<dd>On 09/03/11 11:57, Michael Collinson wrote:<br>
<dl>
<dd>At 12:32 10/02/2011, Andy Robinson (blackadder-lists) wrote:<br>
<dl>
<dd>Henry Gomersall
[<a href="mailto:heng@cantab.net" eudora="autourl">
mailto:heng@cantab.net</a>] wrote:<br>
<dd>>Sent: 10 February 2011 11:07 AM<br>
<dd>>To: Peter Miller<br>
<dd>>Cc: Talk GB<br>
<dd>>Subject: Re: [Talk-GB] Incorrect use of OS VectorMap District
when mapping?<br>
<dd>><br>
<dd>>On Thu, 2011-02-10 at 10:30 +0000, Peter Miller wrote:<br>
<dd>>> On reflection possibly we should use river-bank as that has
more<br>
<dd>>> information in it, but recommend that anyone importing does
a 'bridge<br>
<dd>>> cleanup' at the same time.<br>
<dd>><br>
<dd>>This is an area I'm actually really interested in (for rural
rivers) and<br>
<dd>keen to<br>
<dd>>contribute. So far I've been put off by exactly this problem. Is
a<br>
<dd>reasonable<br>
<dd>>approach to use the OS data for river edges and then fill in the
gaps<br>
<dd>(bridges<br>
<dd>>etc) with OSM data?<br><br>
<dd>+1<br><br>
<dd>If the OS vector data is only assumed to be the banks and the
additional<br>
<dd>data for flow direction, bridges and other features are added
from<br>
<dd>survey/BING etc then we should end up with a very functional
dataset.<br><br>
</dl><br>
<dd>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.<br><br>
</dl>
<dd>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.<br><br>
</dl><br>
<dd>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!<br><br>
<dd>Mike<br><br>
<br><br>
<br>
<dd>_______________________________________________<br>
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</dl><br>
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