[Talk-GB] Multiple coincident boundary nodes. Data quality issue ?

Colin Smale colin.smale at xs4all.nl
Wed Aug 23 09:56:24 UTC 2017

Estuaries are a bit of a special case for the coastline. It is quite
normal for there to be a straight line across the river mouth for some
purposes, but this does not imply that waters above that line are not
tidal of course. 

I think what you are querying, is the link/relationship between: 

a) the high-water line 

b) the coastline 

c) the maritime baselines 

d) the "GB multipolygon"

There are of course many possible definitions of the boundary of GB.
Coastline? (Local) government jurisdiction? Territorial waters? EEZ?
AFAIK this polygon in OSM is based on the coastline, but I might be


On 2017-08-23 10:22, Stuart Reynolds wrote:

>> On 23 Aug 2017, at 09:00, Mike Parfitt <m_parfitt at hotmail.com> wrote: 
>> If the GB multipolygon should follow the high tide line, then the vast majority of the nodes will be situated inshore of those for the administrative/MPA boundaries - i.e. all are normally above the water, except for one moment in Spring.
> The River Thames is tidal as far as Teddington Lock in London. It therefore has high and low water marks, and the high water mark is up against the river walls in London and, even in Southend where I reside at the other end of the river, the mean high tide level is only about 10-20 feet away from the sea wall. Are we honestly suggesting that it is correct that the river is not within the GB boundary? Or, indeed, Southend Pier. Because that would be the effect of the GB boundary religiously following the high water mark! 
> The usual policy (as per OS) is to draw a north south line across the Thames Estuary, which irritates me for other reasons because it is a) artificial and b) frequently rendered, but it is better than a blanket assumption that the boundary must follow the high water mark. 
> Regards, 
> Stuart Reynolds 
> for traveline south east & anglia 
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