On Tue, May 26, 2020 at 6:59 AM Andrew Harvey <andrew.harv...@gmail.com> wrote: > From what I can tell, the ask is a tag for a specific type of way which the > person needs experience or preparedness before undertaking. But I'm lost and > still not completely understanding what exactly this new tag would cover > exactly and what it wouldn't.
I've said repeatedly - but people are not listening - that what's needed is the opposite. More specific ways to tag the hazards of a technical trail is the exact opposite of what I want. A data consumer cannot draw any inference from the absence of a tag. We already have an enormous cauldron of tag soup to describe smoothness, surface, width,incline, steps, visibility, tracktype, overall technicality (sac_scale, mtb_scale), and $LC_DEITY knows what else, to characterize specific hazards. Many of these (smoothness, surface, visibility) have ways to characterize freedom from those hazards. Some (most notably sac_scale and mtb_scale) do not. This lack is _part_ of the problem, so _part_ of what I want is to be able to say something like `mtb_scale=0` or `sac_scale=no` - to say, "this way is non-technical." But that's a very minor issue. i don't think that it's going to work to have to enumerate every possible hazard and assert that a way is free from it. Rather, in general, for a footway, we need a way to assert 'this path is generally OK for a person with less-than-ideal physical fitness or small children in tow." For a cycleway, we need a way to assert, "this path is generally OK for a road bike." This assertion cannot be made by omitting tags. A router cannot tell the difference between 'the mapper didn't say anything about difficulties or hazards', and 'the mapper thinks it's OK.' (Feel free to stop reading here. The rest of this message tries to add detail. The key point is "a positive assertion that the given way is OK for a pedestrian/cyclist of ordinary ability".) ---- The assertion needs to be as simple as possible. which is what leads to the discussion of separating urban paths from technical trails using a top-level key (and the misconception that there's actually a difference between `cycleway` and `path`). I agree with the others who say that train left the station a long time ago, and we're unlikely to catch up with it to board it. What I'm asking for is some minimal set of tags, that we can expect a mapper to provide as a matter of course, to assert that a way is free from unusual hazards. To assert that a walker of ordinary ability, dressed in ordinary street clothes, and perhaps with small children in tow, can use the path. To assert that a cyclist of ordinary ability, aboard an ordinary road bike can ride it. Adding more tags to describe that something does have difficulties or hazards will not help. Emphasis there is also on the word, 'minimal'. What is the minimal information that a mapper needs to provide to let a router draw that conclusion? Obviously, if we were civil engineers assessing trail safety for people with disabilities, small children, or racing wheels, we'd have a lot of formal evaluations to conduct. But if I have to bring a clinometer (or transit and rod, etc.), make the delicate distinction between pea gravel and compacted-mixed-gravel-with-fines, or cobblestone and sett, and so on, before I can say, "this is a regular old path in the city park", it's not going to happen! The best I can do is to presume that whoever built the path did the job, or do the required analysis on a set of ways that's too small to be really useful. The other side of the same coin is that I shouldn't need expert knowledge and a detailed characterization of the hazards to be able to map, "nope! Not going there today!" We enjoy over-classifying everything, and making the fine distinctions is wonderful. But how far would we have got in mapping if a mapper couldn't say, "there's a bridge here" without needing to know the difference between a king-post and a bowstring truss? All of the tags that assert technical hazards are, in the current scheme, trolltags. We've rejected that sort of thing for cars. We no longer say `highway=tertiary demolished=yes` or `highway=tertiary construction=yes` because we recognize that the secondary tag says, "just kidding! You actually can't drive on this!" We realized that routers for cars can't make effective use of an entirely open-ended set of tags that all say, "don't use this road", and we've changed the schema to fix it, with things like the lifecycle prefix. I want the same level of respect for walkers and cyclists. It comes down to two basic questions: - What is the minimum set of information that a mapper needs to assert, to have a bicycle or pedestrian router assess that a way is usable by a pedestrian or cyclist of ordinary ability? - What is the minimum set of information that a data consumer needs to take into account when making that assessment? By paying careful attention to eliminating trolltags, we've nearly answered this question for cars, so our auto-routers like OSRM have become at least passable. We're not nearly as far along with the bicycle infrastructure, and in fact, I first encountered this issue because I was probing with a router to make sure that a major rail-trail in my neighbourhood was routable for bicycles, and found that it would have sent me between two parks on a difficult MTB trail. (I fixed the immediate problem by tagging the trail in question with `surface=ground smoothness=very_horrible`, but I'm not expert enough to assign an `mtb_scale`.) I strongly suspect that most of what is mapped in the pedestrian and bicycle infrastructure lacks some required information. So be it. We can't fix it until we've at least characterized the problem. I anticipate that the next argument will be that the distinction between 'OK' and 'not-OK' is subjective. The only way to have it be objective is to subject every way in the database to a detailed engineering analysis that few of us are qualified to make. (I _am_ an engineer by training. I can state with absolute certainty that assessing a footpath for compliance with applicable standards of construction and accessibility is outside my professional competence, and I am not licensed to certify plans in that domain.) But most of us can make a rough distinction, and even a rough distinction, leaving the corner cases and hidden hazards to the engineers, is better than nothing! -- 73 de ke9tv/2, Kevin _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging
