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building=bridge should be considered a special case of man_made=bridge. Tagging both high-level tags is a violation of One_feature,_one_OSM_element.--Jojo4u (talk) 12:23, 29 September 2016 (UTC)

Wondering if building=bridge was such a good idea - the building in the example picture clearly has a different purpose than being a bridge. If we see a school built the same way it would make more sense to use building=school and either man_made=bridge or just only layer=1 and covered=* or something similar for the road bellow it? But if we would use man_made=bridge for building=school it should not be wrong to use it for building=bridge, sometimes it may be two features in one. RicoZ (talk) 14:06, 2 October 2016 (UTC)
I'm also not happy with this. The example picture does not function as bridge but is built like one. It spans the motorway to save space. I'm strictly against using man_made=* and building=* together, since this is semantically problematic and leads to unpredictable rendering (different style for man_made=bridge+building=*).
What properties does a building=bridge inherits from man_made=bridge? I guess it's the exception we where talking about in covered=*?: The bridge as a whole is both besides (support structure) and over features which are under it. Nevertheless we use layer=1.
I see building=bridge most used for connections between two buildings ( I guess we should look at how to tag this best and not at some fancy buildings like the example.
  • I'd say a skyway is considered building if it's inside is considered indoor. Otherwise it's a man_made=bridge+bridge=covered.
  • About layering: If the skyway is part of building (building:part) and a highway=* goes below it we have three possibilities:
  1. layer=1 for whole building (this does not mean the building is detached from earth)
  2. layer=1 for building:part
  3. layer=1 for both
  4. layer=-1 for highway
  5. covered=yes for highway
I's all about the "under/besides" debate as well here :)
--Jojo4u (talk) 15:04, 2 October 2016 (UTC)
... enough possibilities to do it properly. I think a layer=1 is not sufficient to express that it is a bridge (too many objects have that accidentally) so either bridge or covered or tunnel should enter the scene. The exception could be building:part where it is more expected that some levels like 0 may be missing.RicoZ (talk) 21:05, 3 October 2016 (UTC)
One problem with adding special meanings to building values in particular is that 90% of the values are just niche information about the original use of a building, which is arguably more suited for historical mapping – and then suddenly there is one that needs special treatment in renderers. It's also a relatively rare case, where saving few extra seconds during mapping does not justify special treatment. Let's keep the rules as consistent and simple as possible please. --Tordanik 18:43, 6 October 2016 (UTC)