[Tagging] Verifiability wiki page: "Geometry" section added

[Joseph Eisenberg]

I've added a new section to the Verifiability wiki page about mapping
features with ways or areas when these geometries are not verifiable.

This has been discussed here several times in the past few months, in
regards to tags like natural=bay, natural=strait, place=*, and
proposals like natural=mesa.

Please suggest any improvements to the wording or corrections:
https://wiki.openstreetmap.org/wiki/Verifiability#Geometry

"Linear ways and areas can be non-verifiable if the geometry cannot be
demonstrated to be true or false by another mapper.

"For example, a valley can be thought to refer to the whole area
between mountain ridges, or only to the flat bottom of the valley. In
this case, drawing the natural=valley as an area will usually not be
verifiable, because two different mappers would draw a very different
geometry for the same feature. Many settlements have non-verifiable
borders, especially in rural areas.

"A place=hamlet often lacks verifiable borders. Hamlets in farming
areas often have scattered houses and farms extending outward for
several kilometers. In this case the approximate center of the place
may be well-know, but the outer limits are not clearly determined, so
mapping as an area is not verifiable.

"A natural=ridge can be often be verifiably mapped as a linear way
along the line of the ridge crest. It cannot be verifiably mapped as
an area, because it would not be clear how far down the slopes the
area of the ridge extends.

"Many features which are not verifiable as ways or areas can be mapped
with a single node near the center of the feature instead. In this
case it can be agreed that this node is within the feature, even
though the outer limits of the feature cannot be precisely
determined."