[Talk-GB] Incorrect use of OS VectorMap District when mapping?

[Chris Hill]

On 09/03/11 11:57, Michael Collinson wrote:
> At 12:32 10/02/2011, Andy Robinson (blackadder-lists) wrote:
>> Henry Gomersall [mailto:heng at 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.

-- 
Cheers, Chris
user: chillly