[Tagging] levels and min_level (was Underground / hovering buildings)

Tobias Knerr osm at tobias-knerr.de
Fri Feb 18 12:21:20 GMT 2011

On 18.02.2011 12:04, Peter Wendorff wrote:
> Am 18.02.2011 11:16, schrieb M∡rtin Koppenhoefer:
>>   building_levels should be the amount of building
>> levels. If a building forms a "bridge" like in the illustration, where
>> adjacent buildings have 7 levels, the "bridge" has only 2 levels and
>> the 5 levels below are void, the proposal states you should still
>> apply building_levels=7 and count the voids as levels.
> My purpose with this design of the tagging scheme was something often
> applied in OSM: backwards compatibility.
> Most people tagging level counts of buildings I think would not think as you describe for "bridges".
> As bridges do not appear alone and instead are always part of a building including the sides of the bridge, the building as a whole would have been tagged with building_levels=7. 

The need to apply backwards compatibility to this issue at all arises
from another design decision that I'm not convinced of:
That building parts are tagged as buildings.

In my opinion, the better choice would be to invent a new tag for
building parts, and map the entire building's outline as building=yes in
addition to the individual parts. This would provide an obvious place to
tag information related to the entire building, independently from
similar information related only to a building part. Information in this
case can be the number of levels, but also things like names (it's not
entirely uncommon for building parts to have names of their own that are
not the same as the name of the entire building).

Tobias Knerr

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