Surface=fine_gravel - is it for loose gravel or duplicate of surface=compacted

There’s a good description of the history of the expanded gravel tag on the Australian forum here. Short extract, “ TL;DR: Looks like a non-native English speaker individual created a continuum of of sand - fine_gravel - gravel in 2008 when sand - gravel - rough_gravel or just sand - gravel would have fitted the vernacular better. Never discussed or challenged…”. Lots more follows. I can’t comment on the veracity of this summation but my interpretation of it is that there may never have been a specific intention to include ballast specifically, instead the definition may have been expanded somewhat inadvertently. Who knows. Anyhow, the link is well worth a read.

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I use “compacted” a lot in for Australian and Swedish roads. To me, compacted is a method going back to (European) roman times of having a layer of mud with embedded fine gravel fragments for cohesion and traction. Unless it has been very recently maintained, there is little or no LOOSE gravel. A hard surface is created. So for cycling or trying to drive a motor vehicle at speed, it is an entirely different experience to a gravel road of any kind. So definitely “fine_gravel” is for small loose gravel and does NOT equate to “compacted”.

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Thanks Ture
So the current wiki definition of gravel (4-8cm) does not match road construction practices or use of the English language in Sweden or Australia.

OK here’s my suggestion. Mappers will not be required to make a judgement about whether a road is compacted or not (though we expect that most are compacted). There are 3 classifications based on the largest and most obvious particle sizes, large_gravel >40mm, gravel 20mm and fine_gravel<5mm.

In addition smoothness Key:smoothness - OpenStreetMap Wiki can be used to account for weathering and surface looseness.

gravel should not be used for >40mm any more
compacted is a synonym for gravel (20mm) but its use discouraged

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I don’t know where this information comes from, but if you make the base of a road out of mud with fine gravel in it, you will sink into it every time it rains. You don’t get a weatherproof substructure by using mud. A compacted road base is constructed like this:

Furthermore in most cases a road base is made up of different layers, rough material underneath and finer material on top. Layer by layer is compacted by vibration roller or plate, creating a hard surface which you cannot brush away by hand. In most cases at the end of the process there are some loose pieces of gravel scattered over the surface which do not disturb any traffic. The better the quality of the road, the less loose material is visible. Here is a very good example of a high quality compacted road:

(yes, I have linked this before, did not want you to search :slightly_smiling_face:)

This kind of road, although “compacted” is commonly called “gravel road” in many areas of the world (title of this pic: Gravel Road in Kalkkinen, Finland).

I agree that it may be difficult for a lot of mappers to make a difference between “gravel”, “fine gravel”, “sand” and “compacted”. We are mapping lots of different objects and not everybody can be expert for everything. At least for Europe one can say that practically all roads open to the public are compacted, no matter if sealed or unsealed, and in many countries this does even apply for forest roads and major agricultural tracks. So we could easily say “let’s tag all these (unsealed) roads as gravel roads, that is the common term anyhow”.

But the issue of this topic is not the construction type of these roads but the surface, and there is does well make a difference if you ride your bike on a nicely compacted surface, a rough gravel surface or a surface of fine gravel (as already confirmed by @Matija_Nalis earlier). So even if not every mapper may make up the difference properly we should nevertheless provide the tags to enable a correct tagging at least. And moreover there should be a complete and illustrated documentation in the wiki to make the differences as clear as possible. That is why I highly appreciate the effort of @Mateusz_Konieczny in this matter.

To my understanding it would not be too difficult to distinguish between

  • compacted = a dense and firm surface you cannot brush aside by hand, with none or few loose gravel scattered on top (as to be seen in the sample pic linked above). Easy and smooth bike ride.
  • gravel = a surface more or less completey covered by loose gravel of different size from 2 up to some 50 mm (and more), either produced like that (low price) or emerged out of deterioration of a former compacted surface. Sample pic above “Tamsa” road. Rough and shaking bike ride.
  • fine gravel = a surface completely covered by fine gravel of sized in between 2 and 8 to 10 mm. Sample pic by @Matija_Nalis #14. Sometimes difficult to ride by bike due to “sinking in”, depending on the thickness of the gravel layer.

If the road is subject to corrugations or potholes and the like these tags can further be refinded by adding smoothness=*.

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Imho the surface tags are referring to the man_made object and as such I would not support a tag surface=pine_needles or surface=leaves. If you look at a littered road in a neglected suburb you would not tag this surface=rubbish, would you?

Depending on the surface underneath the needles I would tag “compacted”, “gravel” or “fine_gravel”. If there is no constructed track underneath but just natural ground, I would tag it “ground”, as in a forest the foliage or needles are part of the natural environment.

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where wiki claims such definition?

we are not trying to define what values mean and dictate how people should use it - far too late for that

we are trying to find out how fine_gravel is used in practice

compacted has actually clear meaning and deprecating it helps noone

compacted is a distinct surface and is actually used for that

gravel is sadly often used where compacted is correct value and for massive range of grain size

in many cases you succeed with this, especially where soil/mud depth is not great

+1 to that

Mateusz_Konieczny where wiki claims such definition?
Tag:surface=gravel - OpenStreetMap Wiki “This tag has very large meaning range. Used for cases ranging from huge gravel pieces like track ballast used as surface … gravel may refer to road where track ballast”

“a layer of mud with embedded fine gravel fragments … in many cases you succeed with this, especially where soil/mud depth is not great” this is where a photo would help, I have difficulty understanding this description, I suspect the problem is subtle shifts of meaning between different speakers of English. Maybe it is describing a compacting mix of particle sizes ranging from dust to “fine gravel fragments” as the largest particle size, the size not being specified.

I think it is difficult defining fine_gravel, consolidated and gravel because there are multiple variables that people are trying to capture including:

  • state of maintenance varying from a surface you cannot brush aside through to covered by loose gravel
  • largest or typical particle size
  • uniform particle size which won’t compact vs a mix of sizes which will
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I would tag it “ground”, as in a forest the foliage or needles are part of the natural environment.

earthen ground becomes compacted if it is used a lot, is this compacted or still ground? Is ground a valid value for rocky surfaces?

To my understanding the meaning of “compacted” is compaction by use of machinery on man_made tracks, not a compaction which happens by vehicles or people using a track and that fits to the description in the Wiki.

According to the Wiki ground is an unspecified tag for different kinds of natural surfaces. I am using it when the surface of a natural track is mixed or changing frequently (earth, roots, grass and weeds, mud, rock or stone patches). For reasonable stretches of homogenous surface it may be better to split the way and use the more specific tags but in many cases this would be too laborious imho considering that tracks with ground surface are the lowest category (grade 5).

@Map_HeRo Thank you for filling in better details about construction and emphasing the difference between the construction method (hard for most of us to correctly identify) and the surface and its like impact on different types of traffic (easy visual inspection, and for most of us the main value of mapping it).

A big +1 to your definitions. They are certainly something I’d be happy to use:

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That depends on where you live. In Australia about half of the unsealed public roads are not compacted they are just the underlying native materials.

compacted is for cases where gravel is compacted into a hard surface (one of better tests is what happens when road gets a bit wet - is it turning into mud like with compacted earth? or is it less affected like with gravel compacted into smaller gravel and earth?)

If I would inventing names I would have compacted_gravel and loose_gravel as surface names and without gravel due to “gravel road” used in many areas for roads that should be tagged in OSM as surface=compacted

Maybe also surface=track_ballast for rare cases such as

Surface=fine_gravel - is it for loose gravel or duplicate of surface=compacted - #20 by ElliottPlack had quite nice example with

I have seen cases where repeated refilling with gravel and heavy foot traffic, without dedicated rolling machine, created surface=compacted

I see, so this is likely not “compacted”, or is it?


A surface like this might become mud after lots of rain but will remain firm with just a little rain

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that seems to be a clear case of surface=earth or surface=dirt - plants trampled revealing soil below it, without any gravel in it.

Will turn into mud after rains, may become slippery after little rain - but as it is on a slope and soil become quite compacted it will likely not turn into mud quickly.

(argh, what an unfortunate naming - sadly it may be too late to rename compacted value. Still, maybe it should be shown as “Compacted gravel” for example in iD and other places showing custom labels rather than raw tag values? I will need to check how StreetComplete shows it.)

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surface=compacted surface=fine_gravel
smoothness=* 11.87% 14.78%
smoothness=intermediate 5.18% 7.69%
And smoothness=intermediate is defined as:

This sounds like a reasonable definition, but I doubt that it properly describes previous mapping habits.

To be honest, I think the image currently used to represent surface=compacted is better in every way.

that looks like intentionally rolled one, I was responding to request about surface=gravel converting into surface=compacted without deliberate rolling but by result of use (though maybe that linked image was rolled - I am not familiar with story in this specific case, but it looked close to some where I know that transition happened gradually)

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I believe that a reasonable part of all unsealed roads is tagged as “gravel” or “fine_gravel” by error anyhow so I would not really bother about redefining this values. There are lots of forest roads in my area and when I startet mapping here I checked the actual tagging and saw that most of them were tagged surface=gravel (and very few as fine_gravel).

When I checked the “surface” main page of the Wiki defining a compacted surface as “fine_gravel” I thought “well, that is what they want” so I started to use “gravel/fine_gravel” as well. It took me some time to realize that apparently there is no real consensus about the use of this key. In meantime I startet to retag most of these tracks to compacted as that is what they represent.

I think everything would be fine if there were proper descriptions combined with good sample pics for the discussed surfaces in the Wiki. No need to invent new tags, those available are more than enough to ensure a reasonable tagging for 99,9% of existing roads. For sure that would not exclude wrong tagging in the future but it would be helpful anyway.

+1 and the picture currently used for “fine_gravel” shows a nicely compacted forest road as well.

The picture by @ElliottPlack would also do as sample for compacted and I am sure there is a compacted base layer benath this surface. You would not get a surface as even and plain as in the pic by merely dumping some gravel and sand on a base layer of mud or earth and then wait for the traffic to compact it. (Btw. what can be seen in this pic is normal gravel, not fine gravel as suggested by ElliotPlack).

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I am often thinking of this very topic whilst out jogging, hiking, or biking around and like to take photos of those phenomena. I set up a category on Wikimedia Commons called Category:OpenStreetMap Surface Tagging Examples and added twenty exemplary photos of some of what we’re talking about here.

Here are a few of my favorites:
I’d call this surface=gravel

Gravel trail in a nature area
Elliott R. Plack, CC0, via Wikimedia Commons

The snake for @Map_HeRo and @Mateusz_Konieczny

Snake Crossing the NCR Trail Worms Eye View
Elliott R. Plack, CC0, via Wikimedia Commons

Here’s a surface=fine_gravel

Wet Fine Gravel Trail
Elliott R. Plack, CC0, via Wikimedia Commons

A better shot of the pine needle trail

Pine Needle Covered Trail
Elliott R. Plack, CC0, via Wikimedia Commons

Gravel or Fine Gravel?

Gravel Trail at Hart Miller Island
Elliott R. Plack, CC0, via Wikimedia Commons

And finally, surface=sand without question

This is not a roadway
Elliott R. Plack, CC0, via Wikimedia Commons

One More! This is compacted sand. It is solid until you turn or it gets wet. I’d call the firm parts compacted and sand where it is slippy or spread into loose piles.
Sandy trail on a Gravel Bike
Elliott R. Plack, CC0, via Wikimedia Commons

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