Hello,
I never thought about this before and it would open up a totally new way
of tagging things. But I have some questions/comments:
1) How does this exactly work and do the usual applications expect this?
E.g. would it work to add a tag to an otherwise untagged way that refers
to a relation with the tag "highway=residental" and the way would be
rendered correctly?
As I can't remember any such usecase and couldn't find one: Is there an
example where this is already used?
2) I feel like this is not really the intended use of a "relation" as
this does not really "relate" objects but rather works as a sort of
"category" or a way to define individual collections of tags. I can see
the advantage of having such a shortcut, but for me it doesn't
intuitively fit together with the current definition/use of relations.
3) If this were used more widely, i.e. users would use relations to
group tags that can be applied to many similar objects this might lead
to some more problems:
Possibly individual users would create their own relations with their
often used tag combinations, which probably results in a lot of
identical relations (empty relations with the same tags). Actually I
wouldn't know how to search for an empty relation with a set of tags,
but maybe any of you do.
Also one would have to strongly document these relations e.g. in the
wiki to prevent the creation of duplicates and make them accessible for
new mappers. This would result in them being sort of proposed "tag
collections" or "tagging helpers". Interestingly similar approaches
already exist for some special cases (e.g. "crossing=zebra" is a
shortcut for the tags "crossing=uncontrolled" and "crossing_ref=zebra"),
but of course the difference is that tags are here not explicitely
included. While this might faciliate things for experienced taggers
(that know the corresponding relation numbers or where to look them up)
it is very unintuitively and hard for new mappers. A more intuitive way
would be some sort of "user created tags" that do exactly the same
thing: collect tags and values into a new one that can be referenced by
it's name (rather than some arbitrary number). Of course this would
require major changes in the whole way OSM tagging works (which I do not
want to propose here)
So although relations can (probably?) do this, I don't feel like using
them this way would be good.
Generally I think this is a topic that needs a lot more discussion
before I'd encourage anyone to use such empty relations, especially as I
couldn't find any documentation except for the one wiki site you provided.
Kind regards
pbnoxious
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