Borders on coastlines

Hi. I tried posting this to the mailing list, but it’s been stuck in the spam queue for 5 days, so I’ll try here instead…

I have observed that most admin_level=4 borders will extrude into the seas/oceans and that where this is done they are tagged with maritime=yes. Great!

However, some state borders hug the coastline. Should these also be marked as maritime=yes?

I ask because I am building vector tiles from OSM features and I’m unable to differentiate between inland & coastal state borders and end up with results like this:

One thought I had is that they should be merged with the coastline data. But I don’t like this. At least in the Mexico examples I’m looking at the coastline data doesn’t seem to be official and is quite poor and in some places it would be an improvement to have the coastline match the border. But in many other places the coastline is more accurate and to merge with the border would be a regression.

Alternatively, if the coastline hugging borders could be marked as maritime=yes (or some other applicable tag) it would solve my problem (and be much quicker). Is it reasonable to mark these borders as maritime? If not, is there some other tag I could apply to allow me to filter them?

The presence or absence of tags is controlled entirely by the mapper. Any heuristics need to be applied by the data consumer, as there is no filter that automatically applies these to submitted data.

My question is about the applicability of the maritime tag to borders that hug coastlines. Can I add it? If not, is there some other tag I can add?

Where there are different bits of data that “probably should be the same thing” but one’s obviously more accurate than another I’ve tended not to merge them, unless I know that the “looks to be less accurate” one is defined in terms of the “looks to be more accurate” one.

In the case of Mexico the borders were imported a year or so ago (by Telenav I think) but I’ve no idea about the coastlines. I also have no idea how boundaries are defined at the coast (mean high water? mean low water? something else?) so I probably wouldn’t join them.

Incidentally, this OSM forum is fairly low volume - as well as the various mailing lists (I remember the Mexican one having about half of the regular Mexican “chat” - from memory there was another proprietary forum with the rest) there’s also OSM’s help site which is great for “how do I do this” questions.