[OSM-talk] the ref:color schema

[Greg Troxel]

Iván Sánchez Ortega <ivan at sanchezortega.es> writes:

>> In the US, the essence of the issue is that we have Interstate highways,
>> which have a standard sign, but some states, especially California, have
>> variants, and people want maps to show the local variants so they match
>> what's on the ground.
>
> Here in Spain (where this proposal comes from) we are in a very similar 
> situation. The national scheme is quite clear, but lately, some regions* are 
> starting to colour the road sings their own way just to "stand out".
>
> * Technically, "autonomous communities"

This sounds like a different issue than the main coloring, but maybe
related to why it's hard.

>> The proposal is to tag the road as being an interstate in California so the 
>> renderer can find the interstate/california sign variant.
>
> The main problem I see with this approach is the complexity of the rendering 
> rules. There will be soooo many exceptions to the general rules that 
> modifying the renderers will prove to be a daunting task.

I am also starting to think that the US proposal to do "us_i_ca" for
california interstate is maybe not the right answer.  The road really is
"network=us_i" but maybe needs a "network:sign_variant=us_i_ca" tag.

>> Using ref:color means that has to match ref.  So there's the question of
>> when a physical stretch of road has two route numbers. (This happens 
>> often in the US and I would think it must be common in Europe as it's
>> hard to avoid without having people not to be able to follow the lesser
>> road.)
>
> That's hard to find in europe AFAIK. There are the E-* signs, of course, but 
> we have int_ref for those. Here in Spain, any big road sign will tell you the 
I am not comfortable with int_ref; it seems to say there is a two-level
hierarchy only and it seems the world is much more complicated.

As an example, near me in the US you can be on a road which is both I-95
S and Massachusetts state route 128 south.  Then there is an
intersection where I-95 splits off.  After the interchange you are on
128S and I-93N.  This is funny that N/S are different, but the general
case is quite common.  Near me you can be on SR 117W, and then SR 62
merges in and you are on 117W/62W and then a few miles later there is a
light and you can choose to turn left to stay on 62W or straight for
117W.  But I think once you move to refs on relations and not on ways,
this is no problem.

>> I guess my biggest question is if the colors are arbitrary or they are
>> encoding some property of the road.  If they are telling people
>> something about the road, then perhaps those rules are what should be
>> encoded and then renderers should have access to the
>> (jurisdiction,property)=>color table.
>
> The color encodes jurisdiction and administrative level. The problems I see 
> are:
>
> - Sometimes, there are more real administrative levels than OSM
> administrative levels (i.e. yellow vs. purple tertiaries in Soria).

That sounds like something to be fixed, although it seems
primary/secondary isn't fully about administrative levels - we have
state highways tagged as motorway because they physically are.  With
network="us_sr_ma" or whatever, more levels can be added to describe
reality.

> - That table can be a *real* mess.

Sure, that's the best argument for needing to encode colors.  It just
seems like if one can encode the administrative level etc. and map to
colors that's far better - maybe there needs to be a databsae of the
mapping that all renderers and other users can get at, sort of logically
part of the database but not a node/way/relation.
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