Don't render high(local) administrative borders on coastlines

[matthijsmelissen]

Don't render adminlevel 8 boundaries if the coincede with coastlines.

See also https://trac.openstreetmap.org/ticket/2670

[MattBlissett]

(I was about to file a new issue, but found this old one.)

This is particularly noticeable in Denmark, where adminlevel 4 and/or 7 boundaries are rendered around every fjord and island — I confused them for footpaths last weekend! I think this is very easy to do along a coastline, where it's very reasonable to expect a long-distance footpath.

https://www.openstreetmap.org/#map=12/55.7230/12.0537

https://www.openstreetmap.org/#map=18/55.83414/12.05230

(More generally, the administrative borders are very prominent, yet sub-national borders probably aren't relevant to most map users. How about just making them as thin as possible?)

[kocio-pl]

Are you willing to make some code implementing this change?

[matthijsmelissen]

This is an instance of #3102 (which was quite a heated discussion). This is likely not trivial to accomplish.

[MattBlissett]

Oh wow, I don't really want to open a can of worms here.

I now see #1248, which I think is a better description of the issue I had confusing admin borders with paths.

[kocio-pl]

If I remember, the main problem were proposed changes to the tagging borders, not the rendering. If this one would not mean such changes, it wouldn't be hard to deploy it.

[matthijsmelissen]

There are two types of tagging: tagging the relation that includes all boundary lines of an admin area, of tagging the boundary lines themselves. We render based on the first approach (relation), and people have a problem with rendering based on the second approach (boundary lines).

However, whether a boundary is maritime or not is stored in the individual boundary lines, so if we render based on the relation, we have no access to that.

[jeisenbe]

Would it be possible to use some comp-op "majik", as with the admin boundaries, to hide the dashed borders on the coastline? Eg as in #1107 by @matthijsmelissen

[jeisenbe]

If #4092 is merged we would have ways for the coastlines in the database, which might make it easier to solve this issue for admin boundaries with precisely follow the coastline