[Tagging] boundary=administative on ways

[Brian M. Sperlongano]

>
> - (3) both tags on ways, without relation
>

This style of boundary tagging (a closed way with no boundary relation)
should be regarded as explicitly harmful for technical and data consumer
reasons.  It creates an ambiguity in the case of boundary relation
exclaves.  Consider a city boundary shaped like a doughnut, where the
boundary area is a ring, and the inner ring is a different city.  If the
inner city is tagged as a boundary, it is ambiguous as to whether that
tagging refers to the inner city, or whether that tagging is duplicating
tagging on the outer city's relation.  The inner city might not even be a
city, maybe it's an unincorporated area.  Perhaps that inner ring is tagged
boundary=administrative + name=OuterCity Boundary.  Without the rule that
all boundaries must be relations, a data consumer might interpret that
situation as "there is a city here named 'OuterCity Boundary'," which of
course would be incorrect.  As a data consumer of boundaries, I will speak
very strongly against such tagging.  Thankfully they are rare, and I always
upgrade them to relations any time I encounter them for this reason.
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