[Tagging] Are we mapping ground on OSM?

Christoph Hormann osm at imagico.de
Sun Jul 5 10:38:05 UTC 2020

Generally speaking you touch a field where established tagging in OSM has gaps.  A few notes on that:

We have established and usually quite consistently used tags for a number of fairly specific natural or semi-natural non-vegetated surfaces - natural=bare_rock, natural=scree, natural=shingle, natural=sand and natural=mud and more specifically in coastal environments natural=beach, natural=shoal, natural=reef and natural=wetland + wetland=tidalflat.  It would therefore be rather counterproductive to introduce a new umbrella tag engrossing those like natural=bare_ground.

We have missing tags for bare ground of fine or undifferentiated material.  natural=till has occasionally been suggested for undifferentiated glacial debris.  For any new tag a verifiable definition would be the main problem.

Dry lakebeds are unfortunately tagged quite inconsistently in OSM.  The following variants are the most common in my experience:

* natural=wetland - this is almost universally wrong since most dry or intermittent lakes only feature a water saturated but not water covered ground for a very short time of the year and are otherwise water covered (natural=water) or dry.  That disqualifies them as wetlands.
* natural=mud - usually wrong for the same reasons.
* natural=wetland + water=lake + intermittent=yes (and possibly salt=yes) - this is usually right in case there is regular or at least frequent verifiable water cover.

We lack a suitable tag for dry lakes with no verifiable presence of water (where there is either no present day water cover or so sporadic or incomplete that it is not practically verifiable).  There are a lot of options for tags for these but most of them have their quirks.

Generally mapping bare ground beyond the specific established tags mentioned earlier is often hard without local knowledge.  Imagery taken during dry season will often read like bare ground while there is often fairly extensive plant growth (like natural=grassland) that dries up and looks indistinguishable from bare ground even on high resolution imagery.

Christoph Hormann 

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