[Tagging] building:min_level, building:max_level, min_level, max_level

Tobias Knerr osm at tobias-knerr.de
Mon Oct 8 15:39:23 UTC 2018

On 08.10.2018 15:55, Martin Koppenhoefer wrote:
> Version A is used and defined here:
> https://wiki.openstreetmap.org/wiki/Key:building:levels
> https://wiki.openstreetmap.org/wiki/Key:building:min_level
> https://wiki.openstreetmap.org/wiki/Simple_3D_buildings
> Version B mentions the tags for buildings, but doesn't specify the details:
> https://wiki.openstreetmap.org/wiki/Simple_Indoor_Tagging
> Do we really need 2 ocmpeting tags for this?

These aren't intended as competing tags, but as complimentary tags. A
perfectly mapped building (indoor mapping + outdoor 3D modelling) should
currently use both sets of tags. The tags mentioned in A are used for
describing the outer shape of the building, whereas the tags from B are
used for indoor mapping.

These different use cases result in somewhat different conventions for
the tags:

- A is only counting above-ground levels (because only those can be
verified without entering the building), whereas B includes underground
- B allows for things like "skipped levels", to reflect naming
conventions chosen by the building owners, whereas A is strictly about
counting levels, and does not take local customs for naming levels into
account at all.

The goal of mapping both is to match up the outdoor and indoor
rendering. Or putting it differently, it answers the question which
floor should be visible behind which row of windows.

Of course, we can imagine alternative approaches for achieving this. For
example, there could be some kind of tag that explicitly expresses
"outdoor-level 0 corresponds to indoor-level -1". If we find a solution
for the problem that's easier to understand and use that the currently
documented one, it may be worth considering. But the S3DB building:*=*
tags on their own are not a suitable replacement for Simple Indoor
Tagging's min/max levels.

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