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

Peter Wendorff wendorff at uni-paderborn.de
Mon Jul 30 18:12:44 BST 2012

Am 30.07.2012 18:58, schrieb Paweł Paprota:
> Hi Peter,
> I understand what you're saying about ease of use but at the same time I
> am very concerned about the quality of data - it is clear from reports
> that there are just so many errors that the ref data is virtually
> useless for navigation or location purposes.
But what leads you to the assumption that the data get's better when we 
agree to only use ref on relations or only use ref on ways?

I think, this would lead to a situation where the error count doesn't 
decrease, but the remaining errors aren't detectable any more.

Having refs only on relations means for a data consumer: I have to use 
this data and I have no idea if it's correct - I have to assume it is to 
use it.
Same for refs only on ways.

refs on both means: I am free to use this or that - that's not worse 
than the two other options above; but on top of that I am able to check 
if both taggings are in conflict, and if so, I e.g. may ask my users 
what's correct here, and as osm is free for everyone, as long as that 
one agrees to the contributor terms and license, it's very welcome that 
errors are fixed or reported by these consumers or their users.
> I feel like there is no clear contract between the data and the
> consuming software - some people use "ref" on ways, some people add
> relations (this is preferred now as I see from remapping efforts). I see
> two ways to "fix" it:
> * Invest time in QA - like reporting, auto fixing bots etc. so that the
> relations and refs on ways are synced.
While fixing bots aren't a good approach here - you don't know for sure 
if the relation or the way are correct - this is the way most of the 
current QA tools work now: use heuristics or validity checks to guess 
where errors might be, and most of these tools are welcome and (some) 
mappers sometimes look into it to hunt down data errors.
> * Choose one way (relations is clear "winner" here), invest time into
> making consuming software support this way and clearly encourage it.
-1 as described above: we lose the possibility to check for clear bugs.


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