Proposal talk:Natural=wadi
What this proposal mostly (if i ignore the usual weasel words - like: typically, many, may be) describes is the geomorphological setting of an alluvial plain. This would, in principle, be a viable thing to map and have a distinct tag for. The proposal so far, however, is not providing much of a guidance to mappers how to identify and delineate alluvial plains. Generally speaking OSM has, so far, very few geomorphologically defined tags in wider use, which is partly because they are not as straight away to identify on the ground as tags characterizing surface material - like natural=sand, especially in settings with vegetation, human influence or later non-fluvial modifications of the surface (like through aeolian processes).
It might also be a good idea to think about filling the gap in bare ground surface mapping that currently exists for unsorted, unconsolidated material (consisting mostly of alluvial deposits and till) independent of the geomorphological structure this is part of. Locally mapping the bare ground material is much easier (and practically also much more popular among mappers) than mapping the geomorphological setting. Unfortulately so far mappers often engross unvegetated unsorted alluvial and glacial deposits under natural=sand/natural=scree/natural=shingle because of the lack of more fitting options in tagging. --Imagico (talk) 09:22, 23 April 2024 (UTC)
- I completely agree that it would be good to fill in the gap in tagging for unconsolidated material. We have natural=sand which is widely used and misused. But there are few instances of natural=gravel, no instances of natural=cobble, and scant use of natural=boulder_field. That's something I think about frequently since many of my local trails are in unconsolidated marine terraces which would best be described as cobble. It might be nice to have tags describing unconsolidated surfaces for the entire range of ISO classification. --B1tw153 (talk) 14:42, 23 April 2024 (UTC)
- My comment was not about missing grain size ranges, it was about missing tagging for unsorted material compositions in bare ground surfaces with components ranging from commonly finer than sand (silt, clay) to coarser than sand. These are a common occurrence in alluvial and glacial deposits including a large percentage of alluvial plains in arid/semi-arid regions that this proposal seems to be concerned with. All the photos shown in the proposal feature this kind of material. --Imagico (talk) 19:59, 23 April 2024 (UTC)
- That's an interesting distinction. I'm definitely in favor of having richer tags to be able to describe and map natural features. How would you consider the case where the material in the wash is essentially the same composition as the banks of the wash, just more recently disturbed and not as settled? Here's an example. It might not be completely apparent in the picture, but if you put a shovel into one of the banks, what you'd get would be the same unsorted, unconsolidated material as in the wash.
- Without knowing the specific setting it is hard to tell for sure what the local situation is. The foreground in the valley this is quite clearly the kind of unsorted alluvial deposit i was talking about. The hill sides, however are not the same - you can clearly see substantial exposed bedrock here but you can also see substantial vegetation and therefore likely significant (though thin and patchy) amounts of soil with considerable organic components. It might even be substantially greener during wet season. Overall, this would IMO qualify as a sparse scrubland, in micro-mapping mixed with some bare_rock and scree, but not bare ground overall. All of this refers to mapping local surface characteristics, not the geomorphology or landforms. --Imagico (talk) 21:17, 23 April 2024 (UTC)