[Tagging] Feature proposal - RFC - ele with units

[Minh Nguyen]

Vào lúc 21:21 2021-12-02, Yves via Tagging đã viết:
> It's a terrible idea to change an existing tag meaning.
> If Joe mapper use tags in its favorite editor using presets, this change 
> is useless.
> If he or she knows its tagging, it is pointless.

I think you mean a special field, as opposed to a preset, which is a set 
of predefined tags with a name. In theory, a special field could solve 
the problem of feet measurements going into ele=* without specifying a 
unit, but the forced conversion would lose some precision or introduce 
false precision. That kind of thing keeps some people up at night. Then 
again, there have also been imports that converted feet to meters and 
arbitrarily rounded to the nearest centimeter. [1]

These are things that have been happening for years. Meanwhile, other 
mappers have carefully input feet with the right number of significant 
figures and the unit specified, but would we regard their work as less 
valid for that reason?

> Inconsistencies between ele= and ele:ft= is a chance for QA tools to 
> spot something that needs fixing.

True, I gave some extreme examples of inconsistencies in the proposal, 
but actually, relatively few features are tagged redundantly with both 
ele=* and ele:ft=*. More features are tagged with just feet in ele=*, 
and an unknown number are tagged with implicit feet in ele=*. It's my 
hope that aligning an exceptional ele=* key with the other, more typical 
height keys will enable editors and data consumers to avoid 
special-casing it. They can have a little more trust in the value, 
regardless of the unit in the original source data.

[1] 
https://wiki.openstreetmap.org/wiki/Portland,_OR_Bldg_import#Tag_Mappings

-- 
minh at nguyen.cincinnati.oh.us