[Tagging] The actual use of the level tag

Lionel Giard lionel.giard at gmail.com
Tue Jan 22 09:47:47 UTC 2019

As pointed out for underground station, the building outline doesn't always
cover the underground levels (i.e. the underground levels can extend far
beyond the building limit (and potentially under other buildings/roads...).
We find this problem for metro station, train station or other buildings
like mall.

One example is the mall "L'Esplanade" (Louvain-la-Neuve, Belgium) that you
can see indoor mapped (except parking levels) here
https://openlevelup.net/?l=1#18/50.67045/4.61647 .
It is on a concrete slab (only pedestrian traffic) that cover all the city
center and is more or less 2 levels above the streets where car drive (the
streets are in a "tunnel" when going under the city center. Most of the
time these 2 levels can be described like "street level / ground level" and
the "first level" is for parking, and the "second level" is at the surface
with the pedestrian area) and you have building going up to 6-7 floors
above that. But for the mall, you have a different leveling : the street
level is still the parking entrance, but the two levels above with shops,
so that means that the "first level" of shops is below the surface, and
indeed it is extended below two plazas and another building. To avoid the
mess that could occur with the levels tags, we choose to set an arbitrary
level tagging for the whole city center that's on the concrete slab (it can
be seen as a large building, and it is not too far from reality).

In this case, the level tag need to be synced with all the neighboring
building that are built on the same structure (the "concrete slab"),
otherwise you would have multiple objects at the same position when
rendered on a map. Ex : The mall is officially labelled as "-1" for the
parking entrance, "0" and "1" for the shops levels (the level 1 is on the
surface), while the building that's on top of some part of the mall have
level starting at "0" (the surface level with entrances from the concrete
slab) and going up to level 6 above that. If we use these local numbers for
the level tag, any tools would render the building surface level at the
same position than the shops level that's underneath it !!! For POI it
would be like "is it at level 0 in the mall or at level 0 in the building
?", thus an arbitrary level for all these buildings is really needed to
avoid such problems.

So, i'm really in favor of the level=* for a "data user friendly" tag (that
could correspond to local numbering, but not always) and a special tag for
the local levels. At this moment i would see a *local level tag *like
"level:ref=*" or "loc_level=*" (like we have for name and loc_name ?) but *on
each object*, as it would not be realistic to use an outline in the cases i

PS: i hope my example is not too confusing, or badly explained. :-)
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