[Tagging] Clarification on the role link in route relations

[Dave F]

On 08/01/2022 23:02, Minh Nguyen wrote:
> Vào lúc 14:27 2022-01-08, Dave F via Tagging đã viết:
>> On 08/01/2022 21:02, Minh Nguyen wrote:
>>> This is a high enough number that it can't be dismissed as a mere 
>>> tagging mistake, yet it falls far short of the 766,473 
>>> highway=motorway_link ways, let alone other highway=*_link ways. [8]
>>
>> I think there maybe a misunderstanding of the difference between 
>> route relations & ways upon which route relations are placed.
>>
>> The link role of a route relation can be placed on *any* way. It's 
>> commonly used as an indicator for 'this is the way to go to get to 
>> the route' and not just connections between different routes.
>> In the UK National Cycle Routes have signs for this with the ref 
>> number in brackets. (Roads also have this scheme, but IMO roads 
>> determined by their reference numbers are not valid route relations)
>
> Can you provide an example of what this looks like? How does it differ 
> from what destination:ref or destination:ref:to would be tagged on? 
> (destination:ref:to is for where a trailblazer sign says "To ABC 123" 
> with an arrow, as opposed to just "ABC 123" with an arrow.)
>
> The current documentation for "link" explicitly states that it's for 
> link road connections between different road routes, making no mention 
> of recreational routes. I think it's unlikely that U.S. mappers, at 
> least, would support comprehensively using the "link" role for 
> anything that so much as mentions a road route, considering that there 
> are more maintainable representations of that information. There are 
> countless "To ABC 123" signs that are many miles away from the route 
> itself, with nothing in between mentioning the route. Here are some 
> examples tagged with destination:ref:to:
>
> https://www.openstreetmap.org/way/19051231
> https://www.openstreetmap.org/way/48889597
> https://www.openstreetmap.org/way/60108744


These are tags on ways, not route relations.
Again, I think you are misunderstanding the purpose of route relations, 
which are journeys, taken over multiple different types of highway.

Your examples above appear irrelevant to route relations.
https://www.openstreetmap.org/way/19051231

destination:ref: The 'I 275 North' is the *only* road that highway goes 
to. Competent routing software doesn't need to be informed of that.

destination:ref:to: The 'I 75' is miles away. If these refer to road 
signs, then it has nothing to do with route relations. There are many 
turn-offs. A driver's destination could literally be anywhere.


>
> My point is that the downsides seem to outweigh the upsides with 
> regard to road route relations

If you mean where highways with the same reference number have been 
collected together into a  route relation, then I agree with you.
There's no point in them as their reference number already groups the 
ways together.


DaveF