[Tagging] [OSM-dev] Multiple values "warning" in P2

Alan Mintz Alan_Mintz+OSM at Earthlink.Net
Thu Jul 26 11:00:46 BST 2012

[Moved from dev]

At 2012-07-26 01:42, Richard Fairhurst wrote:
 >Alan Mintz wrote:
 >> Semi-colons are the agreed-upon way to provide multiple values for a
 >> field. It seems wrong to "warn" of their use, especially given the
 >> demonstrated potential to cause users to "fix" such values incorrectly.

 >In most cases having two values in a field is undesirable. Virtually no data
 >consumers will correctly parse them: if you have a node with
 >amenity=pub;cafe, it will generally not be recognised as either a pub or a

I often have to tag retail and food/beverage shops with multiple values. 
Until someone comes up with a different solution, likely requiring a 
wholesale renaming of keys and values, I believe the consensus solution is 
to use multiple values. The subject has certainly been beat to death a 
number of times, with no other solution coming out of it. Isn't it time the 
consumers caught up? Not that we are supposed to be tagging for the 
renderer anyway :)

 >P2 does have a small whitelist of tags for which it won't warn about a
 >semicolon and I'm happy to consider adding to that, if you have a particular

I would suggest that it should instead be a blacklist for the particular 
case you mention here:

 >I suspect however that what you're really talking about is the ref tag and
 >that's a little more complex. In some countries (such as, I think, Britain,
 >France and Germany) then a road genuinely can't have two numbers (excepting
 >E-roads); in some it can (US, Poland). So at the least any solution here
 >will need to be bbox-specific.

and not in the US, since multiple ref values are still apparently correct, 
necessary, and common.

In my case, the issue recently came up with source (and source_ref) keys, 
which I routinely tag with multiple values in order to correctly cite my 
sources. These certainly don't matter to any consumers (except humans).

 >But I'd welcome opinions (ideally on tagging@, not here)

Moved from dev.

 >Are route relations not a better solution for those
 >places where roads regularly have two numbers? Would we not be better off
 >fixing our osm2pgsql/Mapnik setup to render refs from relations, rather than
 >telling P2 not to warn about, essentially, deprecated behaviour?

I don't agree that it is deprecated. If people are still tagging that way, 
regardless of admonitions about tagging for the renderer, they will likely 
continue to do so until the renderers change.

I would not be against a more specific warning about the route case 
(depending on location), but having a general warning about something that 
is not currently generally wrong does not seem correct, and has the 
demonstrated ability to cause users to do the wrong thing.

Alan Mintz <Alan_Mintz+OSM at Earthlink.net>

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