[Tagging] Data redundancy with "ref" tag on ways vs relations

Paweł Paprota ppawel at fastmail.fm
Mon Jul 30 17:22:44 BST 2012


Hi all,

As part of the Poland remapping effort I have implemented a reporting
system called OSMonitor which analyzes road network in Poland in OSM
data and produces reports. Recently one user requested additional
validation - checking if ways in a relation for a specific road contain
proper "ref" tag values (where "proper" means that "ref" on ways
includes "ref" from the relation).

This is what came out of OSMonitor:

https://wiki.openstreetmap.org/w/index.php?title=OSMonitor/Poland_Major_Roads&oldid=791535

Note the error named "relation contains ways with wrong ref". So for
some roads the ways contain multiple variants of "ref" value. More -
"ref" tag for ways is out of sync with relation membership, see
http://www.openstreetmap.org/browse/way/172192711 (I am referring to the
version 2 of this way in case it has been fixed in the meantime) for
example.

So the question is - why does "ref" on way level make sense at all when
there is another (better and more flexible) way (pun intended) of doing
things?

Of course there is no hard rules in OSM concerning tagging but
http://wiki.openstreetmap.org/wiki/Key:ref does not say too much about
the problem above. I think it should describe why relations should be
used instead of "ref" tag on ways if possible.

I understand that software that consumes OSM data (renderers,
navigation) probably uses "ref" on ways but as you can see from the
report - it is useless for most of the roads (in Poland, don't know
about other countries) and relations contain more up-to-date information
so the software should use relations in the first place.

What do you think?

Paweł



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