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

Peter Wendorff wendorff at uni-paderborn.de
Fri Feb 18 12:53:33 GMT 2011

Am 18.02.2011 13:21, schrieb Tobias Knerr:
> 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.
Yes, it could be a good idea to invent a separate tag for building parts.
I would appreciate that (and initially these issues are part of the 
reason why my proposal is not a proposed tagging scheme in the common 
sense of the proposal process).
But one question is left here:
What is the building outline you would like to map in future as 
building=yes, too?
Is it (a) the "maximum size outline" as shown in aerial imagery?
Is it (b) the "on-ground-outline" a pedestrian would be able to go along?
Is it (c) the "maximum size outline" including underground parts not 
build up above ground - like bigger underground parking areas?
Is (d) the building=yes a fallback for renderers not supporting the 

Each of these possibilities has it's advantages:
A blind pedestrian would benefit from (b) as that's the "barrier" 
outline and the leading lines he can percept with his cane.
A airplane pilot woult benefit from (c) as it corresponds to what he can 
A mapper using aerial images as a source would have the easiest job with 
interpretation (c) as that's exactly (given that the aerial is exact) 
what he can see at the images.
>   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).
Yes, there are additional arguments to change something here.
Feel free to do so - that's the reason why it's not yet a "real proposal".


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