Re: [Talk-GB] UK coastline data

[Colin Smale]

On 2019-07-14 08:49, Mark Goodge wrote:

> 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: 
> 

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. 

It's a government decision (within certain rules), but I am still
searching for the legislation that defines these specific lines. I am
working on the assumption that they are somehow connected with the
baselines used to delineate areas of Internal Waters and Territorial
Sea, but I am not entirely confident. 

This transposes the UNCLOS rules into UK legislation, but does not give
the actual locations of the Baseline: 
https://www.legislation.gov.uk/uksi/2014/1353/made 

This shows the limit of the Territorial Sea, which, interestingly, does
not always correspond to the OSM data: 
https://data.admiralty.co.uk/portal/apps/sites/#/marine-data-portal/items/2bd3ea1bbdc04e83bb9fb54644723d20?geometry=-16.516%2C49.719%2C16.048%2C54.439


This shows graphically where the straight baselines have been applied: 
https://data.admiralty.co.uk/portal/apps/sites/#/marine-data-portal/items/0b5d3be5acba43578230019a4f2df95d


I note that the limits are much further seaward than I was expecting; in
the Thames estuary the line is roughly from Herne Bay to Clacton, for
example. This doesn't align with any admin boundaries I know of.___
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[Talk-GB] weeklyOSM #467 2019-07-02-2019-07-08

[weeklyteam]

The weekly round-up of OSM news, issue # 467,
is now available online in English, giving as always a summary of all things 
happening in the openstreetmap world: http://www.weeklyosm.eu/en/archives/12232/

Enjoy! 

Did you know that you can also submit messages for the weeklyOSM? Just log in 
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[Talk-GB] weeklyOSM #467 2019-07-02-2019-07-08

[weeklyteam]

The weekly round-up of OSM news, issue # 467,
is now available online in English, giving as always a summary of all things 
happening in the openstreetmap world: http://www.weeklyosm.eu/en/archives/12232/

Enjoy! 

Did you know that you can also submit messages for the weeklyOSM? Just log in 
to https://osmbc.openstreetmap.de/login with your OSM account. Read more about 
how to write a post here: 
http://www.weeklyosm.eu/this-news-should-be-in-weeklyosm 

weeklyOSM? 
who: https://wiki.openstreetmap.org/wiki/WeeklyOSM#Available_Languages 
where?: 
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Re: [Talk-GB] UK coastline data

[Mark Goodge]

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: 



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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