[Tagging] Removal of rendering for waterway=wadi

[Joseph Eisenberg]

It is proposed to remove the rendering of waterway=wadi from
Openstreetmap-carto, the style used in the "Standard" layer on
openstreetmap.org - see
https://github.com/gravitystorm/openstreetmap-carto/pull/3931

As discussed back in January 2015, the tag waterway=wadi is ambiguous,
because it is was used both for dry valleys and for intermittent
waterways. See https://lists.openstreetmap.org/pipermail/tagging/2015-January/thread.html

http://wiki.openstreetmap.org/wiki/Tag:waterway%3Dwadi has been listed
as deprecated since then.It is recommended to use
waterway=river/waterway=stream + intermittent=yes for waterways,
natural=valley for valleys.

Since that time the usage of waterway=wadi has dropped from 18,000 to
6,000, while intermittent=yes + waterway has increased from less than
800k to over 2 million now.

Please comment on
https://github.com/gravitystorm/openstreetmap-carto/pull/3931 if there
are any problems with dropping this tag.

Also consider checking your areas for features that might be more
clearly tagged with natural=valley or waterway=stream/river +
intermittent (usually this takes local knowledge of the area, so it is
not recommended to retag features which you have not visited in
person).

- Joseph Eisenberg