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 <[email protected]> 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 <[email protected]> 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. > >
_______________________________________________ Talk-GB mailing list [email protected] https://lists.openstreetmap.org/listinfo/talk-gb
