On 09/03/2011 11:57, Michael Collinson wrote:
At 12:32 10/02/2011, Andy Robinson (blackadder-lists) wrote:
Henry Gomersall [mailto:[email protected]] 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.
Mike
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Interesting point Mike.
There are similar issues about tracing from imagery or using Vector Map
District when doing other waterbodies: reservoirs are the ones which
immediately come to mind. Often the landward side of the splash zone is
more obvious than the usual water level, and if that is used for mapping
it gives a false impression. Patches of riparian scrub and marsh also
seem to be treated inconsistently by the OS (perhaps aerial interpretation).
Most larger rivers will have flood-level gauges (right word?) which
might be some kind of aid for choosing a 'natural' level to map, but
sourcing then is not straightforward. I've only done a bit of mapping by
wandering around in wellies with one foot on dry land and the other in
the water.
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