[Talk-GB] UK coastline data

Edward Catmur ecatmur at googlemail.com
Thu Jul 11 22:37:09 UTC 2019

Tricky - it appears to be a rule that all the famous sea caves are
accessible by foot at low tide (there's probably a geological reason, like
why sea cliffs tend to have a ledge below exposed at low tide). That said,
some sea arches have inward-sloping sides - e.g. Stair Hole
https://www.openstreetmap.org/node/2128418334 on the 1:25000 the HWM and
LWM both appear to follow the outer edge of the arch above while the
interior is rendered with the cave/cave entrance symbol.

It's an interesting question how to map sea caves and natural arches - all
I've looked at so far have the coastline running along the outer edge of
the land above, but OTOH you have natural arches like Rainbow Bridge
https://www.openstreetmap.org/way/569676595 mapped as an area natural=rock
with Lake Powell running uninterrupted underneath it; and Natural Bridge
https://www.openstreetmap.org/node/4325038750 is mapped as two cliffs, not
intersecting the creek or path beneath.

On Thu, Jul 11, 2019 at 9:56 PM Colin Smale <colin.smale at xs4all.nl> wrote:

> Good point. Do you know of one? Let's have a look at how the OS deal with
> it.
> On 2019-07-11 22:52, Edward Catmur wrote:
> On Thu, Jul 11, 2019 at 9:19 PM Colin Smale <colin.smale at xs4all.nl> wrote:
>> * Where the coastline is essentially vertical (harbour walls, steep
>> cliffs) MHWS and MLWS can coincide in OS data (sharing nodes but not ways),
>> but of course low water can never be landward of high water.
> Is this necessarily the case? Couldn't an overhang result in a low water
> landward of high water? Consider e.g. a sea cave that is flooded at high
> tide.
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