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

Peter Wendorff wendorff at uni-paderborn.de
Tue Jul 31 10:01:29 BST 2012

Am 31.07.2012 10:33, schrieb "Petr Morávek [Xificurk]":
> If he knows for sure, that on that road from point A to point B is 
> ref=42 and not ref=56 as the OSM data says, then the user should fix 
> it as I wrote in previous email. Remove the ways from the current 
> relation and add the correct ref tag to the ways themselves, or create 
> a new relation for them. Problem fixed! 
now we have a relation that's incomplete again - how to use it? A 
continuous road it isn't any more - but that was one major pro argument 
for the relations before.
So I can use it to - well... make downloading a complete road/route more 
easy, but then we're again in the problems we had months ago: use 
overpass or sth. like that for that purpose.

The user "fixes" the problem by creating a new relation for parts of the 
old one, removes correctly the now changed elements from the old one and 
the new relation get's a ref attribute.

It's hard to see these changes. While it may be easy to detect that the 
route is broken now, and that someone removed elements from it, it may 
be hard to detect the new relation, as it does not have to be created by 
the same user or in the same changeset.
But even if other users are aware of these changes and come to the 
conclusion, that in fact the whole route has changed it's ref... They 
merge both relations again to one (old or new - doesn't matter) and 
change the ref to the new, now correct one.

What's the benefit of that new relation?
Drawbacks are more load on the osm infrastructure, and I cannot see any 
benefit in detection or at correction of the introduced errors.

> Note, that if the edit was mistake after all, then QA tool analyzing 
> road network should catch that. 
How should it do that?
> If he's not really sure about his data, but wants to alert locals 
> "hey, here may be something wrong", then he should use FIXME tag as 
> for any other dispute.
FIXME isn't for dispute, but for "I don't know how to change it or I 
don't have the time to do so now."
> -- If I understood your scenario correctly, it can be summarized as: 
> "Let's use conflicting ref tags for road disputes instead of fixme 
> tag." Personally, I don't support this view.
No. I never said something like that.
I didn't ever talk about intentionally create conflicts; that in fact 
can be done better by fixme tags.
I talked about an intrinsic fixme along with fixing the local bugs, 
where the individual mapper is not aware of the overall situation in 
wider scope.

And: I'm talking about mappers who are able to add a tag to a way, but 
are in fear of touching complex stuff like relations.

If you ever worked with mappers who do mapping in their spare time and 
are not digital natives, programmers or database geeks, you will have 
seen some who don't touch stuff as soon as it's too complex: Better keep 
the wrong data than to break something that of course is cool, but I 
don't understand why it's cool and how it works.


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