I've so far stayed out of this discussion because my final thoughts on
the matter will I am sure be contentious.
In no order of importance my thoughts are:
1) the idea of basing a the limit on coastline on levels of salinity or
average water flows makes as little sense as trying to specify that the
"landuse = forest" tag can only be used when there are a specific number
of trees growing in a particular area.
2) yes the wiki says coastline should be based on the Mean High Water
Spring, but I've long argued that for instance no one in London would
say they lived on the coast even though the River Thames is tidal
upstream of the city. Hence the border between coastline and water body
should be downstream of the tidal influence and is based on "a
reasonable estimation of where an observer might suggest the river ends,
and the sea begins". Such an estimation is imprecise, not subject to
verification, and different observers will have different opinions - get
over it. As in point (1) different observers will have different
opinions on where a "forest" ends and "scrubland" starts.
3) Due to the needs of the rendering process we have long established
that ways tagged "natural = coastline" are a special case.
4) We have existing tags for "tidal = yes" and "estuary=yes",
"admin_level = ?" which means it is unnecessary for the coastline tag to
be used as a proxy for these.
5) The discussion on what the tag "natural = coastline" actually means
has been discussed for so long that it appears almost insolvable.
Given the above.
A) In view of all the points above it is not possible to write a concise
definition of what the tag natural = coastline" represents.
B) Until January 2020 we had a reasonably broad agreement on where the
coastline should be. Though I recognise, perhaps more than most who
have contributed to this thread, that there are still are large number
of ways ( particularly in the more sparsely populated areas of the
world, or where the OSM community is not large) that are unchanged from
the position they were placed in by the PGS imports in 2006.
After much thought my, probably contentious, view is:
1) We should establish an agreed "OSM Coastline position", which I
suggest would approximate to the position of the coastline on 1 January
2020.
2) Any edit which moved the position of the coastline by more than 20Km
from the established position should be classed as vandalism, unless
such movement had previously been agreed by the community.
David
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