Admin Boundaries: botched import?

[hroest]

Bug description There are currently tons of administrative boundaries in OHM that were imported from OSM (I believe) and are incomplete / misleading. Instead, we should have a clear description of what administrative boundaries should look like and remove those that got imported and/or add start_time to those.

I think the problem was when coastlines and rivers got imported, some of them carried the tags with them, e.g. admin_level= and boundary=administrative. However, with only some of these imported and without the relations that link them together, we now have a ton of "split up" admin boundaries all over the place that sometimes render and sometimes down (depending on whether they are joint or not). Btw: these are all part of changeset 1, which should have been stripped of admin_level= and boundary= tags.

Repro Steps

1. Go to https://www.openhistoricalmap.org/#map=8/-51.980/-60.628&layers=O
2. Observe admin boundaries for falkland islands that are present even in Roman times!

Screenshots & URL Falkland islands around 100 AD: there are British borders all over them:

[jeffreyameyer]

@hroest's suspicions are correct. There are many points or ways with tags that were not removed, but should have been, as part of the initial import. We need to do a planetwide cleanup...

[hroest]

I looked at this with overpass queries and it seems mainly to be coastlines and rivers. It is not so hard to do and its a few thousand ways (at most). For example

way["admin_level" = 4]({{bbox}});
(._;>;);out;

yields about 5374 ways of which only 130 have a start_date -- however its more complicated as a relation associated with the way may have a start date. I dont know whether there is an easy way to filter those that come from changeset 1 but these would be the ones we would want to remove. Alternatively, we could attempt to globally remove admin_level= and boundary= tags and hope that people use relations for most of them and not closed ways.

Hmm: I already see that people dont use relations always https://openhistoricalmap.org/way/198200370 so it wont be as easy since also new content would be affected.