On 02.12.2022 13:31, Alex wrote:
Paths and ways along a road can be mapped separately in OSM, but those separate geometries cannot be identified as part of the road, or only with the significant effort of using geometric processing (which most applications can't perform).
I strongly agree with the concept of tagging information that is hard or impossible to compute accurately or reliably. I want to emphasize that from the start since the objection has been raised in multiple discussions that something is theoretically computable. I would rather that we not obstruct valuable tagging because the same information could theoretically be computed by some brilliant algorithm not yet constructed and/or extremely detailed tagging, that in combination would require significantly more effort than just tagging the desired information in the first place.
Therefore, a sidepath concept using the tag "is_sidepath" as an additional tag on ways (in particular cycle ways or foot paths) is proposed to indicate whether a way is related/attendant to a road (i.e. adjacent and parallel to a road) or whether it runs independently/isolated without any relationship to a road. Furthermore, an extended set of sub-tags is proposed to allow to explicitly tag important road attributes on the sidepath itself.
_Mainly_, I have concerns about the concept of a cycle path or foot path being attendant to or a sidepath of another road.
In Norway, we no longer have cycle paths and foot paths. We have cycleways, footways and carriageways. It may seem like a small difference in terminology, but it makes a large difference as part of an overall mindset. Roads are roads, and different types of roads are simply meant for different types of travel.
To me, this proposal sounds similar to a hypothetical proposal that we start tagging roads that runs adjacent to railroads as "is_sideroad=yes". It makes very little sense to me to establish the railroad as the "primary" line of travel and the road as an "attendant" line of travel. Just because they are parallel does not mean there is a meaningful relation or hierarchy between them.
I'm concerned that this type of tagging establishes and codifies a hierarchy, a relative importance, and an implied dependence, that I don't see in many of the posted examples, and that I'm not aware exist in formal road structures.
An exception of course is if the road was specifically built to facilitate access to the railroad by non-rail means, and the road was tagged as such, it would make sense to relate it to the railroad it serves.
I know the term "sidepath" exists and is used, but I can't see that it is semantically different from cycle path, cycle road or cycleway, except for this rather vague property of somehow being an add-on to the "proper" road.
Can you provide any thoughts on how you see the "is_sidepath" relationship in principle?
_Additionally_, I'm curious about what you will do with the tag. I've read the use cases, but I don't fully understand them. Perhaps you can elaborate?
Rendering: How and why would a renderer treat a cycleway differently when is_sidepath=yes?
Routing: How does it help routers to know that a cycleway runs parallel to a carriageway? If the preference is to ride on cycleways, I assume the router will pick the cycleway regardless. If there is no preference, I assume the router will pick whichever line is shortest.
I see a value in being able to capture a name.Data analysis: How is capturing the quality of a cycleway obstructed by the lack of an is_sidepath tag?
_Finally_, I agree that any use of is_sidepath or similar conceptual tagging, like in the railroad access road scenario, seems most valuable when it actually includes a direct reference to the other line. Simply knowing that there is a line out there that is parallel and adjacent to this line seems like very vague information. Duplicating some information from the related line seems a bit odd, because it still leaves no way to automatically tell which line we're trying to reference. But I guess it can be hard to implement a direct reference in practice, if the two ways don't have exactly matching line segments?
Cheers, Jens
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