[Tagging] Equivalence relation

[Georg Feddern]

Peter Wendorff schrieb:
> Am 11.01.2011 04:26, schrieb Steve Bennett:
>>  On 11/01/2011 12:20 AM, Richard Mann wrote:
>>> I put adjacent=yes on the highway=cycleway, so the user of the
>>> cycleway=track tag on the main road can ignore ways with adjacent=yes
>>> on them. The user who'd prefer to use highway=cycleway ways doesn't
>>> know that the cycleway=track is a duplicate, but routers only have to
>>> give a slight preference for highway=cycleway over cycleway=track to
>>> use the "right" one (and even if they use the "wrong" one, it doesn't
>>> much matter anyway).
>> IMHO, this is being extremely optimistic about the powers of a 
>> router. So you're saying that a router could see the "adjacent=yes", 
>> then locate a nearby cycleway which is "adjacent" in some way, and 
>> conclude that the two refer to the same thing?
> I think you think too complicated here.
> In much cases Steve could be right.
> The routing engine has not to consider explicitely the adjacent-tag.
> The slightly preference of the separate tagged way over the tag, 
> compared with the usually equal lenght of both alternatives will push 
> the routing engine to prefer the cycleway explicitly tagged.
>

+1

> But: While routing engines will work well this way, renderers could fail.
> A renderer has to check if there in fact is the separated cycleway to 
> be "allowed" to drop the tag for rendering. (If it's the target to 
> render cycleways).
>

If the corresponding highway=*, cycleway=track is also tagged with the 
adjacent-Tag, router and renderer can choose in general, which sort of 
way they use - without any need for locating them.

Regards
Georg