[Tagging] tagging capitals

[M∡rtin Koppenhoefer]

By looking at the wiki and taginfo, as well as some data as Cardiff /
Wales, it doesn't seem clear which way capitals should be tagged / are
currently tagged.
There is proposals to use capital=yes together with admin_level on a
node, there is the idea to tag capital=2 (according to admin_level but
incorporated in the capital key), and there are several relations
proposed.

Looking at the data it seems clear that a national capital should be tagged
capital=yes

Regional capitals are mostly not tagged at all with a capital key. I
suggest to keep capital=yes for national capitals and use e.g.
capital=4 for the capital of an admin_level=4 area. This would keep
consistency in our data and allow at the same time for simple
evaluation.

What do you think?

Cheers,
Martin