[Talk-GB] Boundary_line at the coast

[Borbus]

Hi Edward,

On Sat, Sep 7, 2019 at 10:08 PM Edward Bainton <bainton.ete at gmail.com>
wrote:
> 1. Does anyone know if county boundary lines at the coast are set at
> mean low water? There's a gap between coastline (which I understand is
> MHW) and the county boundary:

Most, if not all, of the boundaries in OSM are from OS OpenData. They do
generally follow mean low water spring (MLWS), but there are bound to be
exceptions in some places. I'm not sure how quickly they update
considering the actual MLWS level changes all the time in some places.

> 2. "coastline" is very coarse - is it ok to make it follow the coast
> more finely, or is it some important legal line where it stands? (I've
> already done this on the east side of the portage, but then thought
> perhaps that was a no-no:
> https://osm.org/go/e7tUNAM7G?layers=D&m=&way=669235281)

You can absolutely map the coastline very finely. It should follow mean
high water spring (MHWS). You can get both MHWS and MLWS from OS
OpenData VectorMap in the "Tidal Boundary" data.  There is a convenient
archive of the data here: http://parlvid.mysociety.org/os/

For an example of both MHWS and MLWS in OSM, see The Wash:
https://www.openstreetmap.org/#map=11/52.9418/0.3049

> 3. Also, there are two walls visible on aerial imagery that all but
> match the doglegged county boundary as it crosses the isthmus. Is it
> safe to assume that these mark the actual boundary, and can I tug the
> boundary to match them? Or maybe assume the boundary is definitive,
> and the imagery is misaligned, so I should move the walls? Or leave
> well alone?

There might be a written description of the boundaries available, like
with public rights of way. That would answer the question if so. I'm
sure someone knows more than me.


Happy mapping,

Borbus.

On Sat, Sep 7, 2019 at 10:08 PM Edward Bainton <bainton.ete at gmail.com>
wrote:

> I'm interested in boundaries marked at Mavis Grind
> <https://osm.org/go/e7tUHqY_g-> (thanks to SK53 for the waterway=portage
> <https://wiki.openstreetmap.org/wiki/Tag:waterway%3Dportage> tag - Mavis
> Grind is an old Norse portage, still in use by Shetland Canoe Club).
>
> 1. Does anyone know if county boundary lines at the coast are set at mean
> low water? There's a gap between coastline (which I understand is MHW) and
> the county boundary: https://osm.org/go/e7tUHoc5F--?m=&way=669235281
>
> 2. "coastline" is very coarse - is it ok to make it follow the coast more
> finely, or is it some important legal line where it stands? (I've already
> done this on the east side of the portage, but then thought perhaps that
> was a no-no: https://osm.org/go/e7tUNAM7G?layers=D&m=&way=669235281)
>
> 3. Also, there are two walls visible on aerial imagery that all but match
> the doglegged county boundary as it crosses the isthmus. Is it safe to
> assume that these mark the actual boundary, and can I tug the boundary to
> match them? Or maybe assume the boundary is definitive, and the imagery is
> misaligned, so I should move the walls? Or leave well alone?
> West side: https://osm.org/go/e7tUHqdxn?m=&way=669235281
> East side: https://osm.org/go/e7tUHrpqY?m=&way=669235281
>
> Thanks as ever, Edward
>
>
>
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