[Tagging] boundary=administative on ways

[Mateusz Konieczny]

There are multiple ways how boundary=administrative and admin_level
tags may be placed

- both tags on boundary relation such as https://www.openstreetmap.org/relation/1435909
- both tags on way such as https://www.openstreetmap.org/way/199228161
As result following methods may be used
- (1) both tags on relation, no tags on ways
- (2) both tags on relation and both tags on all ways- (3) both tags on ways, without relation
- (4) both tags on relation, boundary=administrative without admin_level on way

(ways may also have for example waterway tags, if boundary is defined as
following changing course of a river)

I)
Is there any benefit from using method (4) over either (1) or (2)?
Is there any tool that requires boundary=administrative on ways but
does not need admin_level on ways?

I am asking that question as (4) is used in Poland and there is proposal to remove
this bare boundary=administrative from ways. JOSM, Vespucci and Osmose all
complain about this tagging. And noone wants to duplicate admin_level on ways.

So there is a proposal to switch to "both tags on relation, no tags on ways"
version, and I wonder is there any drawback to such action.

II)
https://wiki.openstreetmap.org/wiki/Relation:boundary#Way_tags
recommends (2).
"Boundary ways should have boundary=administrative and the admin_level=* for the highest border"

Would it be OK to mention that creating relations without duplicating tags is also acceptable?
Or maybe even preferable?

Repeating this info on ways seems to me an equivalent of adding
"highway=motorway" on every node of motorway, or
"multipolygon=yes" on every way belonging to multipolygon.

Note that default map style, JOSM, iD, OSMand all have no trouble with relations
without tags on ways.
(maybe there are some subtle bugs? At least I have found nothing problematic)

I know that ÖPNVKarte requires tags on ways, but administrative boundaries are not 
prominent in this map style anyway (also, I just reported this issue to style author
so there is a small chance that it will change)
https://wiki.openstreetmap.org/wiki/Talk:%C3%96PNVKarte#Boundaries_tagged_as_relation_only_are_not_shown

Is there any good reason to maintain such duplication?

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