There are lines like way 247546324 created as administrative boundaries but tagged to become roads via e.g. highway:unclassified. This strikes me as a bad idea, because users are more likely to nudge roads around to match aerial images (fortunately if a user re-classifies a boundary into a road type, the boundary metadata will be preserved). There’s also the risk that they’ll be left untagged, as nearby way 247545745 was.
Are there any official guidelines about this? Is it OK if the boundary is actually defined by the path of the road?
This isn’t an official policy statement, but I think it is a bad idea to double up in this way. I would have thought there was a strong preference for administrative boundaries to be areas, even though lines are allowed. I would also expect them to have names, that were different from the name of the road (there is no name at all). Boundaries need admin-level tags.
If they are defined by by the centre line of the road, I would expect them to share nodes, but this requires a careful judgement; if the physical road (rather than its map representation) is subsequently modified, will the boundary move with it.
Finally, Bing is not a valid source for an administrative boundary, as we are only allowed to use the non-oblique aerial imagery and boundaries, at best, could only be identified from signs that need to be viewed horizontally, and are probably only really available from government maps.
Thanks for the explanation. If I encounter this again I’ll remove the highway tags and create new roads nearby (or on the same alignment if it’s already correct, but using separate points). That seems to be the usual end state.
I think the Irish community has been dealing a lot with admin boundaries overlaid on roads (townland boundaries) - they might be able to offer “best practice” tips about dealing with it. Maybe ask in IRC in #osm-ie?