i.e., grass but on a stable surface. Often used on parking lots and motorhome stopovers.
Germans call it “Schotterrasen”. I have seen it names “gravel turf”, e.g.,
http://www.schotterrasen.at/e_index.htm
It serves a purpose similar to the “grass_paver” tag but does not fit the wiki description (regular cell structure).
It it important, especially this time of year, to know that you car will not sink into mud, even if there is wet grass.
Should we document “surface=gravel_turf” on the wiki?
Some additional reading material (in German):
I can see the differences to other surface values, but I can also imagine that it is difficult to distinguish them well - especially for non-experts. At what point is it recognized as grass and at what point as compacted?
Yes, it can be difficult to spot, but that is all the more reason to document it in OSM.
The source is mostly municipalities and owners of motorhome stopovers that put it on their websites, signs, information boards, flyers, etc.
Similar to stating whether the water from the water_point is drinking water (which is also hard to distinguish for non-experts although they might find out later).
Users of heavy motorhome stopovers do tend to be experts in these matters. When you park a 7 ton motorhome on wet grass, you will find out if it is solid ground.