[Tagging] The actual use of the level tag

[Tobias Zwick]

> So from a SIT perspective, the problem isn't that the US (and other
> places) call the ground level "1". It's that the level below that is
> called "-1" rather than "0". You could still make it compatible with
> Simple Indoor Tagging by adding a skipped_levels=0 tag to the building,
> but this tag has only been used five times so far.

skipped_levels is also pretty awkward because one needs to recalculate
the indexed (OSM) level from the real (on the ground) level all the
time. Even worse if the levels are not actually numbers on the ground
but letters or something else (like in that mall in Bangkok).

If SIT (and by consensus in the SotM 2016 indoor session) encourages to
use the level numbering scheme of the building operator, why keep the
"tied to numbers" requirement?

Someone mentioned earlier in a diary discussion a pretty nice
solution[1]. So, in a mall with the levels P2,P1,G,M,1-12,14-99 one
simply tags:

- a shop on level M with "level=M"

- the mall building with "levels=P2,P1,G,M,1-12,14-99" (the order of the
  levels). If levels is missing, a numerical order is assumed

- also the building with "ground_level=G" to define which level is
  the ground level. If ground_level is missing, 0 is assumed.

I find this would have the following advantages while completely
compatible with the current SIT scheme and has no disadvantages (I can
come up with):

1. The correct denomination of the floor is always directly tagged on
   the shop -> much easier for end-user apps to display the correct
   floor for a shop because no special SIT software support is necessary

2. no calculating forth- and back between level "indices" and real names
   for the levels (for neither the software nor the mapper) because this
   effectively eliminates the concept of indices:

   a) thus avoids the whole 0-index-based vs 1-index-based problematic
      that I started this thread with.

   b) thus no workarounds like non_existent_levels necessary

What do you think about this?

[1]
https://www.openstreetmap.org/user/Anton%20Khorev/diary/46933#comment43565