building:levels is a different tag with different purpose, so there is no real issue.

was and is already the widely used builiding:levels

I’ve found only 2 proposals with building:levels: Simple 3D Building since 2012 and “Building Attributes” since 2008, but it was partly broken by 2011 and it’s hard for me to say was it widely used or not. Oh, authors of S3DB has broken this tag: “Number of floors of the building above ground (without levels in the roof)” is quite different from “Number of stories, including the ground floor”. Shame on them.

If regionally your level numbering skips 0

In fact, there are (1) buildings on hills with many “ground” levels (2) some buildings have their own floors naming scheme. For example, nearby trading center hit both: floors numbered as “-2”, “-1”, “1” and “2” with parking on “-2” and shops on the others. To make things more funny, floors “-2”, “-1” and “1” are on the ground.

So, from my point of view, ignoring “truth on the ground” principle made level tag broken for indoor mapping without relations and should be forbidden in favor of level:ref.

Simon, in one of the first proposals there was “levels” tag containing ordered list of existing floors. For example “P2,P1,G,1-12,14-99” defines a building without zero and thirteenth floors. In fact, it also allowed to define height of each floor in meters.

Simply adding tag ground_floor=1 gives us a simple way to understand that P2,P1 and G are all underground and we need to render 98 storey building. No mindblowing level calculations, no workarounds for non_existing_levels. 3 years before SITh, just add one simple tag and have superfast rendering as you don’t need to traverse all intersecting level relations or objects, all you need is building itself.