Type of stone in surface (`surface=granite` and similar)

There is noticeable (but not very high) number of surface=granite / surface=marble and other similar tagging type of stone into surface tag.

I think that it would be much better to tag it as a material tag.

Tagging surface=granite blocks distinguishing between surface=paving_stones / surface=sett / surface=unhewn_cobblestone / surface=rock etc.

surface=granite may be any of following

Exposed raw rock (surface=rock)


(file page)

Natural stone machined into a flat surface (surface=paving_stones)

Flattened stone, but still not entirely flat and not covering entire surface (surface=sett)

Raw cobblestone of natural, uncut, rounded stones. (surface=unhewn_cobblestone)

Stones or plates individually arranged in a row, allowing to walk on, surrounded by an unpaved medium such as grass or water (surface=stepping_stones)


Maybe also surface=gravel and surface=pebblestone

(note: specific photos above may be not necessarily depict granite, but surface=granite could also take such forms)

So I would propose to tag material of surface differently - maybe material=granite would work?

So instead of surface=granite use material=granite? For example instead of highway=pedestrian surface=granite tag highway=pedestrian material=granite ?

This would unblock tagging specific form taken by this materials and tagged as surface=paving_stones/sett/unhewn_cobblestone/…

I plan to:

  • edit Key:material - OpenStreetMap Wiki to clarify that material=granite and similar is fine on roads
  • create wiki pages for surface=granite surface=marble and similar high use to describe that tags as not preferred for describing material of road/path surface (including link back to this discussion)

Would it be a good idea?

Note that above applies only to types of rocks and does not apply to some other surface tags describing materials (say, surface=mud that is not a problem as it takes only one form or types of metal where I have not yet thought what would be a good handling of them).

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I agree

Plus surface=whatever-is-suitable-here

Yes, at least for rock formations that should be tagged with surface=rock. Whether it offers an added value to know from which material a gravel is I do not know.

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Yes, that what I meant by “This would unblock tagging specific form taken by this materials.” - I will edit it to be more specific.

No idea whether there is any benefit of tagging that gravel is made out of say andesite, but I have no problem with people putting it into material tag.

Yes, absolutely.

In such cases the tagging would probably be

highway=pedestrian + surface=paving_stones + material=granite

I understand that is what you are going for … :+1:

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highway=pedestrian + surface=paving_stones + material=granite

Based on the paving_stones wiki, this should be:

highway=pedestrian + surface=paving_stones + paving_stones:material=granite

I created Tag:surface=granite - OpenStreetMap Wiki (edits/improvements welcome! Especially for images of granite for each surface, currently only sett is definitely actually granite). I plan to make very similar pages for other rock types of surface in high use.

And edited Key:material - OpenStreetMap Wiki

oh right, because we have also such funny variation

I think there is a demand to be able to distinguish between man-made and natural materials of paving stones (made of fired brick or concrete vs natural stones such as marble, granite, etc.); at least I felt that need myself often. However, I expect that there are very few geologists among us who could correctly identify materials beyond that, and are interested in making such distinctions.

The first image shows sandstone not granite, the locality is called Elbsandstein for some reason :wink:

It is hard to find natural granite surface. I found this, File:Lüsener Fernerkogel (20200115 143514).jpg - Wikimedia Commons - you may not see it on the photo, but yes, there is a path mapped there! Zoom in to see the specific graininess.

PS: This made me update the data of Way: 93361602 | OpenStreetMap - I did not set material=rock but rock=granite instead, as for me, material reminds just too much of something man_made, which this certainly is not. I also felt, there is no path there, merely a scramble instead, thereby risking to re-create something like the highway=busway plunder/debacle by hiding the route from OSM-Carto, and leaving people wondering, how to get to the summit, when no path goes there? Please correct, if such duck-tag-as-you-like runs too much controversial to OSM policy.

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Yeah, I know. Thanks for finding a better one! (many other are not showing granite either and ideally would be also replaced)

Can you take/upload one with more visible path or people walking there?

I tried to find one with more visible path and failed, so far I have File:Коростышевский карьер 2.jpg - Wikimedia Commons

Found one from Category:Half Dome Cables and Trail - Wikimedia Commons

I do not have such connotations, but I am not a native speaker.

The rock @ Yosemite might be Granite, but the trail surface isn’t: To me, that looks like a ladder? People on the trail do not touch the rock.

Unfortunately, where granite is top layer in the area of my local knowledge, it always looks like in the picture and not even a horde of elephants can make a visible path there.

Update, https://upload.wikimedia.org/wikipedia/commons/f/f6/California%2C_Yosemite_National_Park%2C_Half_Dome%2C_hiking_up.jpg rock is actually surface, and from literature, it is granite.

I found one where surface is actually granite (and used it in article) due to a flat section with no need for steps.

I created Tag:surface=marble - OpenStreetMap Wiki

Note that for some I have not found images of specifically marble.
If someone would have good illustration, feel free to improve the page.

I just hope, this “placeholder” methodology used in documentation will not spread to OSM-tagging, so people consciously tag something wrongly, just because they did not know the right tag or no right tag exists.

In plain English, “material” would tend to refer to something manufactured, like glass or plastic or brick, while “substance” would tend to refer to something more raw, like limestone or wet cement. But material and substance already have more specialized meanings in OSM anyways.

I suspect these tags would still creep in because mappers in some cases would be more familiar with the kind of rock than with the way it’s laid. For example, the floor of a highway=corridor may be surfaced in slabs of polished marble. A mapper might regard that as a distinct surface because it’s so slippery. But if a subkey is more correct, the mapper may not discover it on their own without a helpful editor field.

@Minh_Nguyen You are probably the right mind to have answers for a broader subject than creating wiki pages mostly just to deprecate tags: This topic here reminds me of another one I took part of the discussion. I had the idea, to make possible some kind of autodiscovery for consumers of data by chaining in key/value pairs.

I guess, that has inspired me to tag surface=rock; rock=granite for the scramble linked above. When a consumer reads key=value, it can look, if there is a key with the same name as the value, and use it to learn further details. Is that comprehensible?

When there is a path with surface=rock; material=granite, how to know, that the material applies to the surface? It might instead apply to the handrail/whatever other attributes there are?

Yes, a human who looks at the raw tags and sees this combination would know exactly what you mean. I think editing/rendering/routing software would be unlikely to do this kind of traversal automatically for any arbitrary value. For one thing, it could lead to some pretty unexpected results in other ambiguous cases:

  • building=school amenity=school school=secondary (Built as a secondary school or now functioning as one?)
  • building:material=rock wall:material=rock rock=granite (Just one, or both?)

We normally cope with these conflicts by documenting when iterative refinement is expected, but not by expecting it to occur universally. I guess this is similar to the challenge with using unrelated keys like surface and material together. The most predictable version of iterative refinement relies on subkeys, like surface=granite surface:fragment_size=* etc. (I’m making this up.)

Anyways, my point is that surface=granite most likely refers to different things depending on the kind of feature. A granite-surfaced highway=corridor is very likely to be surface=paving_stones (which luckily comes with several subkeys), but the common term for that would be “granite surface plates” or just “granite surfacing”. Since granite is such a durable material, the slabs can get as large as concrete plates (concrete:plates), but the tagging is so different that users may not know about these options.

Like others here, I’m not very concerned about determining the mineral composition of a crushed rock surface.

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I think that touches on something, that concerns OSM tagging a lot: Some tags are introduced by people that care about a certain aspect, from a particular position, and later get used by people, that do not care about that aspect, having no connection to the POV of the tag creators.

Some might wonder, why Yosemite granite looks so much different than Lüsener Fernerkogel granite? (Fernerkogel is surface=rock;rock=gneiss;gneiss=granite; while Yosemite has surface=rock;rock=granite)

In the end, its all gravel? The challenge to replace paved/unpaved with something more specific a lost endeavour?

PS: How about surface=paved;paved=rock;rock=granite vs. surface=unpaved;unpaved=rock;rock=granite?

I would not go so far - even if pebblestone/gravel differentiation that someone attempted failed there is still reliable distinction (I hope) between sand and compacted

Well taken, but surface=rock says nothing about whether it is paved or unpaved rock. Of course, there are the keys tracktype|smoothness :wink: but how reliable is that?