As per: Tag trail_visibility: Proposed Improvements for this Descriptive Tag - #117 by erutan
For me, markers are just one of the many visual clues available to see where the path is. I don’t see why we would want to have a key for path_visibility_if_there_were_no_markers for a marked trail. What is the usefulness of having this information? What’s the use case?
If current trail_visibility as a whole (mix of trail surface and makers) is all we need, then why do we have a separate trailblazed:visibility? Why is the visibility of markers in and of themselves important, but an actual physical path/trail unimportant?
Your argumentation would support the removal of trailblazed and trailblazed:visibility unless you can make a case for why they are more important than there being a physical visible trail surface as they are currently included in trail_visibility. Currently trailblazed:visibility is essentially trailblazed:visibility_if_there_is_no_trail
So trailblazed:visibility only really matters when he has to make a choice between different paths, i.e. at junctions. There it could be useful info (to know how much attention he needs to pay, to know how much time he might need to spend on finding trail markers and on walking down the wrong path, etc.).
Here I don’t think it makes any practical sense to separate markers from any other visual clues: anything that helps to follow the mapped trail (the thin dashed line on the map is what I mean by “path” or “trail”) should be taken into account.
Doesn’t the original definition of trail_visibility (which was accepted at the time) also help when trying to find an intersection? If you have no markers but an excellent clear trail surface junctions are straightforward, if you have no trail surface but a lot of markers and a larger marker at a junction (plus further markers heading in more directions) junctions are straightforward. Is there a clear argument as to why only the latter is important and the first case isn’t? Guideposts at a junction would seem more important than markers in terms of routing.
In terms of pure “being able to follow a route”, overall path visibility is what matters. Trail surface, marker visibility, and overall path visibility don’t always add up - I gave a recent example where surface visibility is horrible, markers are intermediate, that sort of averages out to the overall experience of the path visibility is bad. I can honestly see an argument for just simplifying things and relying on the new trail_visbility and trailblazed without the related :visibility but at the point where people are arguing that trailblazed:visibility is important I can’t see why trail surface is somehow irrelevant.
I have nothing against breaking down trail_visibility further into trailblazed:visibility and trail_surface_visibility. It could be useful for renderers, they might want to show an indistinct but well-signposted path differently from a well-worn but unmarked one. It’s just that I can’t see myself using trail_surface_visibility much: we’re debating edge cases here but for the vast majority of paths I imagine the value will be identical to that of trail_visibility.
It’ll come down to a regional thing, as well as how often people are hiking on abandoned or informal trails.
In areas of heavy vegetation, dirt, or sand you will tend to have paths that express themselves by solely trail_surface_visibility unless you are briefly crossing a streambed or something (wet or dry) in which case there will be markers. In areas of long stone slabs (alpine granite, desert slick rock / sandstone) or consistent snow/ice coverage paths will tend to be driven by markers. In the past few weeks I’ve hiked on areas that were excellent on one and no on the other, and vice versa.
One interesting case are trails that have a good surface visibility, and are occasionally marked where surface visibility is poor so the overall visibility of the path is still excellent. In that case I think just having trailblazed=cairn, trail_surface_visibility=good, and trail_visibility=excellent would tell the story pretty clearly - you will lose the trail at times, but if you look for a marker you can find yourself back on the path again.
Blazes are in no way comparable to a trodden path.
At this point we can have a highway=path with trail_visibility=excellent that has no visible path/trail at all because there are bright tall markers at regular short intervals. I think in that case, pointing out that there is no actual “trail” surface is worthwhile.
I see a few different approaches to this:
A consensus that trailblazed:visibility (the visibility of markers along a path) significantly more important than the visibility of the surface of the trail itself, at which point this is dropped.
The lack of above consensus, at which point this should be adopted given that it passed before, but due to unclear wording has changed over time.
If only the overall visibility of the path matters (which it seems that trail_visibility is now poised to formally become) there should not be a trail_surface_visibility and trailblazed:visibility should be deprecated. The general trailblazed key still provides some useful metadata and seems separate of this discussion.
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Ce sujet de discussion accompagne la publication sur https://community.openstreetmap.org/t/should-we-have-a-trail-surface-visibility-if-trail-visibility-formally-shifts-to-an-overall-path-visibility/98817