[Talk-GB] UK coastline data

Mark Goodge mark at good-stuff.co.uk
Sun Jul 14 06:49:19 UTC 2019



On 14/07/2019 00:39, David Woolley wrote:
> On 13/07/2019 22:21, Colin Smale wrote:
>> So what was your point again about internal waterways? The "extent of 
>> the realm" is not the 12-mile limit, it is ±MLW, isn't it?
> 
> Assuming it is mapped correctly, this is an example of an administrative 
> boundary that is outside the low water mark: 
> <https://www.openstreetmap.org/way/174971215>

Yes, and that's probably a good example of where "the coast" crosses an 
estuary rather than continuing up it.

After all, if MLW was always the admin boundary, then most of the Thames 
through London would be outside local government control. In reality, of 
course, it's part of the GLA and partitioned between various London 
Boroughs. Pragmatically, admin boundaries cross the MLW where 
appropriate to maintain meaningful local government areas.

I don't know if there is an official formula for when admin boundaries 
do actually do this. Looking at boundary maps, it appears to be the 
principle that if opposite banks of the estuary are close enough, the 
admin boundaries cross the estuary at that point and then run up the 
centre (or thereabouts) of the river if the river itself is a boundary 
(which it often is). But I don't know what amounts to "close enough". On 
the Thames, it's just to the west of Southend, as illustrated in the 
above link. On the  Severn, it's just downstream of the Severn Bridge. 
On the Humber, it crosses from Spurn Point. But admin boundaries don't 
cross The Wash, and in Scotland admin boundaries don't cross the Forth 
until upstream of Kincardine. So it seems to be based on what is locally 
appropriate rather than a rigid measurement. Which is something you 
can't map simply by observation; you have to know what the actual 
consensus is.

Mark



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