RFC: hiking_exposure key (along with hiking_technique this disambiguates sac_scale)

This example in Olympic National Park I think illustrates where this would be useful. The first part (3-4 miles) of trail is mostly dirt single track following a forested ridge, then pops out of it into mellow subalpine terrain.

There’s a stretch or two past that where the surface changes to… rock? natural gravel? and it becomes more exposed. I personally don’t care about the surface change, but met a random “everyday hiker” looking man who called it sketchy despite still being SAC T1 / hiking_technique=casual-walking.

It then goes back to being nice mellow single track with very few obstacles before tightening up again briefly (no photos of the second part, it made less of an impression on me).

I wouldn’t obsess over the surface of this, and I can think of one small section that was somewhere between T2-T3 that would be better done as an node obstacle=talus or something vs breaking into a way with a different technique, but I think having these two large sections of trail (hundreds of meters long) with path_fall_risk=long_falls_possible or something would be appropriate.

Tagging them as T4+ feels very inappropriate given the trail itself is easily walkable.

At least in the US climbing community (which I realize isn’t the same as the hiking community), “exposure” refers more to the sensation that there is “a lot of air” under you, and not so much the risk or consequences of a fall. This would be important for people who have an unatural fear of heights, or vertigo.

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Yeah somewhere in this thread it was decided that path_fall_risk is more accurate than hiking_exposure. I didn’t want to update the title as it’d break cross links. :slight_smile: This also makes more sense for multi-use trails - it’s the same fall risk for MTB or horses etc.

I’d put the trail example above as long falls possible (low risk) as that slope is a high enough angle it could be difficult to self-arrest and it cliffs out below in places, but it would be somewhat counter-balanced by hiking_technique=casual_walking, which would be different than that fall risk with hiking_technique=scrambling, It’s definitely not airy_but_safe but you’re not hanging off a wall either.

I think the psyche part captures this:

psyche: many people will still be fine doing this at lower hiking_technique=* levels, but people that are sensitive to heights could be very uncomfortable. experienced people with a “head for heights” will notice the risk but probably not be overly concerned by it.

There is the concept of direct exposure (e.g. knife edge or steep enough to be realistically indistinguiable) and indirect exposure (e.g. you have a ledge under you but it’s a fatal fall below that).

These are all YDS Class 3 (so not climbing climbing), but with different levels of fall risk (photos I have on hand).

I’d put these at short falls

Indirect long falls (the first is less obvious from photo, was taken for composition vs an explainer)

Direct long falls (if still not clinging to a purely vertical face, a loss of traction would have serious consequences)

The distinction between direct and indirect is where I’m having a lot of trouble as that’s not a very intuitive way of phrasing it. Possible vs likely doesn’t feel right but is “simpler” low and high make sense to me.

I don’t like how exposure and technique are conflated in YDS (as they are in SAC). These are all what I would personally call 4 PG (or short fall risk here). I often find people saying that Class 2 under rates an approach, but just because it’s exposed doesn’t make it Class 3 or 4 (or likewise that say King Col is Class 2 but feels like Class 4).

To take a step in the other direction, these are all Class 2, but have significant fall risk

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Ok, thanks. I am new to the forums, although a long time OSM contributor.

That is a good description of my understanding of “exposure.” IMHO it should be a separate tag.

General comment
Love the photos! Looks like a great adventure!

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I’ve been thinking about this proposal over the summer, and think it’s a good idea to remove risks and exposure from sac_scale (hiking difficulty), but not to create a new key for it, because:

  1. We would have to tag a hiking trail with 3 tags for difficulty, visibility and risk/exposure, while afaik it is only possible to render 2 of them. Difficulty is often shown by different colours, and visibility by different dashing. How would differences in risk/exposure be rendered?

  2. We already have other tools to show risks/exposure on maps. I guess hikers will use maps that show altitude lines, and altitude lines close together means steep so dangerous. In addition, we can add natural=cliff, ridge and arete to the map and tag ways with the hazard= key.

Historically, people who have tried to redefine existing OSM keys have struggled, for the very obvious reason that its difficult to explain to every single OSM mapper who uses the sac_scale key that “it’s definition has now changed”.

It is absolutely true that lots of data in OSM has more information stored than would ever displayed on any one map, but I I think you might need to explain what you mean here in a bit more detail. Can you point to an example map that you have made?

Again, a link to an OSM-based router or map as an example would be great.

I’m not aware of any map with sufficient resolution to judge fall risk from contour lines. For example, the USGS topo maps for the area of this trail correctly show a hundred-foot cliff by merging contour lines, but they don’t show that there’s no fall risk. It’s a smooth trail across flat ground, never getting closer than about six feet from the edge. Even if you trip over your own feet, there’s no way you’re going over the cliff.

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Agree! There are quite a few mappers who still use track_type to describe how usable a track is, while the key has changed long ago to describe firmness. I’m in favour of removing the risk element from sac_scale but realise it won’t be easy to get it accepted.

This screenshot (Elevate 5 rendertheme from openandromaps) shows a difficult (sac_scale=demanding_mountain_hiking, red) section of path south of Pas de l’Œille (Way: ‪Pas de l'Oeille‬ (‪37891050‬) | OpenStreetMap ) with trail_visibility=excellent (very long dashes) that is part of a hiking route relation (green edge). I wonder how information on the exposure of this path would be shown on this map? I think in this case there are plenty of other clues that this could be a dangerous path: the fact that it’s SAC T3 (hiking difficulty and exposure do often increase in parallel), the closeness of the altitude lines, and the presence nearby of cliffs and aretes (the dotted grey line near the 2000 m altitude is the famous Arêtes du Gerbier).
IMG-20230914-WA0037 Use of hands, so indeed T3

@Carnildo is right that there are exceptions, but I doubt if they are many and if they are worth developing a new key for that most renderers will choose not to show anyway because they prefer to show sac_scale, trail_visibility and membership of a route relation.

I really think this is missing the point.

I once worked for a car manufacturer who broke models down into body plan, number of doors, engine size, trim and about 7-8 other attributes. What they did not store in the database was the actual model a customer would ask about when they walked into a showroom: the database was totally oriented towards production and not selling cars. I had to write complex logic to present that information to the marketing team, who had to deal with oversupply of certain models relative to demand.

Breaking things down on OSM does not help either mappers (who would have to make judgements about several things) nor consumers who probably desire to show a simple scale for hiking. We should remember that the SAC scale was developed by a major publisher of guidebooks covering one of the most popular countries for mountain hiking and scrambling. I’m sure they considered alternatives, although a six-point scale for mountain activities has been standard in Europe for over a hundred years, so there is widespread familiarity with such concepts.

Such a breakdown may help mappers to judge how to assign a SAC scale, but having 3 semi-subjective scales instead of one is likely to increase rather than decrease inappropriate grading.

As an aside if you want to express hazards, such as exposure, more directly then we already have a perfectly suitable hazard=* tag, which is not well used with hiking trails. It offers a much broader range of possibilities: possible rivers/streams in spate, paths below high tide line, slippery when wet (a common warning for paths in the pre-Alps and many Alpine areas " heikel bei Nässe"), rockfall …

I would much rather we explore what we can do with hazard than introduce more scales.


Austria has a three point hiking scale: easy, moderate, hard. I observe the same in many portals: AllTrails, Komoot, OutdoorActive, e.g.

In essence, the SAC Hiking Scale has 1, 1+, 2-, 2, 2+, 3-, 3, 3+, 4-, 4, 4+, 5-, 5, 5+, 6-, 6 – no idea if there is 1- or 6+ :wink: I am too lazy to count how many points there are.

The Austrian scale recently got a pseudo fourth point: Alpine Route. This is for easy pathless scrambles. Not for hiking paths. Maintainers are in process of swapping guideposts in places where targets only reachable through such were marked simply as “hard”. Will take years. There is no scale for those routes.

Just curious, in the map above, are the blue lines the easy passages, or the harder ones, in respect to the red ones?

Blue is sac_scale=mountain_hiking so easier than the red ones (sac_scale=demanding_mountain_hiking). See Elevate (Wandern, Rad, Sightseeing) - openandromaps

GaiaGPS in the US uses color to show access (foot, foot and horse, foot and bicycle, etc). Caltopo lets you tap on a trail and a drawer on the side shows all the metadata for it.

I thought this too. If a tag is useless because it isn’t displayed directly then we should get rid of surface, smoothness, informal, operator, etc.

It’s developed for the Swiss Alps. 99% of the values are for the first three in the scale, with the vast majority (around 85%, I forget exactly). T1 and T2. It’s very strange marking up a trail in the desert as “mountain hiking” and there’s a lot of confusion around it. I’ll see T1 trails above treeline marked up as T4 in North America because it’s “alpine”.

There’s a lot of ambiguity in past posts in the forum here - a T1 difficulty trail has T4-T5 level exposure so someone wants to tag it as T2. Mixing those things up is a mess. I have plenty of times where I’m on less technical but more exposed terrain, or more technical but less exposed terrain.

This is used in North America, though it tends to vary widely by region and be graded on a sort of local subjective scale relative to things around it. Interestingly I’ve come across people in AllTrails complaining about a short level hike marked as “easy” because it had roots in the trail that were ~T2 so it should have been “moderate”.

As someone who spends a LOT of time with slope shading (I do a lot of what would be similar to the Austrian Alpine Routes). I’ll say it isn’t useful at all for actual exposure risk, it’s not granular enough.

These two photos are from this area of trail. The one with less direct exposure actually looks worse on Topo. This is with the updated high resolution US slope angle shading.

The following XC “route” has more purple shaded terrain (~double the height) using old slope angle shading but it was ledgey enough that I was able to come down it with a T3 / YDS 2 technique and minimal “short fall” exposure. Going up was T4 / YDS 3 and that’s how I’d describe it.

My favorite example of slope angle shading on topo would be this spot near Squamish BC

In terms of how to display it, icons on the trail would work. Direct exposure could be a diamond with a vertical line in it, indirect exposure could be a square with a line that is initially more horizontal that then goes vertical.

I’m not opposed to using hazards for this, but natural=cliff doesn’t indicate if the trail is 3cm or 3m from a cliff edge (likewise ridge or arete). The closest value on hazard=* which exists is falling rocks which isn’t appropriate. It’d be better than the current use case where it’s impossible to extrapolate exposure since it is mixed in with technique.


I think there’s a few different cases that would need to be addressed:

  1. A brief moment of exposure on a trail seems totally appropriate for this (and should be used even if there is a separate exposure key for ways/paths). I think in this case being able to differentiate between direct and indirect exposure would be useful, so that would be two values at least. Short falls could probably be ignored in the sense of being called out on topo vs being metadata for a path.

  2. For longer stretches of exposure, how would hazards work? Would there be two tags that act as bookends (start/stop, open/close) or would it just be a hazard tag every 5-10m.

Knowing that 200m of trail is exposed is different than a 5m section. Having two hazard tags 200m apart could look like it’s just two brief spots but having 20-40 hazard tags seems messy.

It is funny that the tags are from a Swiss scale and the colours are from an Austrian scale. Is there any renderer that uses the Swiss colours? [Apart from the JOSM SAC mapcss plugin; in the lower grades, that is.]

PS: In the 2023 SAC Hiking Scale, SAC scale and SWW colour are no longer identical. I made some changes to the Wiki, somebody even noticed :slight_smile:

My main problem with this proposal is that it is for no good reason activity specific, why can’t it just be “exposure” and not imply that hiking exposure is different from the same on a via ferrata or on a mountain bike, or whatever.

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Why not add a heading Hiking related hazards to the Key:hazard wiki and create hazard=exposure, etc.?
To the wiki for sac_scale we could then add that it is assumed that hiking risks increase with increasing sac_scale, and that for path sections that have an unexpectedly high risk that is not evident from other information on the map, a tag from the hazard key can be added. It is then up to map renderers to decide how to display that information (probably one “danger” symbol if the section is short, and one at each end if the section is long).

Someone from Australia came in and was expecting exposure to be exposure to the elements (so lack of tree shade etc). It’s a somewhat mountaineery term so fall_risk seemed more straightforward as a suffix and moving the prefix to path solves this issue as mountain bikers etc face the same exposure.

update: see RFC: hiking_visibility key 🍿 paired with hiking_technique and hiking_exposure/fall_risk this rounds out the hiking path trinity - #3 by erutan


That seems reasonable to me.

Looking at https://wiki.openstreetmap.org/wiki/Key:hazard again it seems like it’d be simple to have a single node for a very tight spot, and then a way like it’s currently used for landslide.

I’ve found on and off talk about having foot/trail specific hazards for years in various places in OSM. If this thread pushes that into action it’ll have been a success (and it helped me think out how to describe off-trail routes outside the scope of OSM).

Want to take an initial stab at it? :slight_smile:

Here’s another example where looking at topo lines doesn’t give you an accurate idea of exposure. Gotta love how the river flows up and then back down a 100 foot saddle. It’s not uncommon for opentopo in the southwest to be a bit off (though not as badly as this).

topo and old slope angle shading (derived from the same old shuttle data)

topo and new slope angle shading (I corrected some ways in this area so the trail shows going through here now, there’s some that are clearly just a few nodes with staight lines going to them but I haven’t been there to verify):

maps and reality did not match:

view from below (which matches old USGS maps and new slope angle shading)