[Tagging] Using multipolygons to map bays in Alaska
Eugene Alvin Villar
seav80 at gmail.com
Sun Nov 18 04:54:39 UTC 2018
I have been following this discussion with interest since I would also like
to have bays and straits represented by some sort of polygon/area instead
of just nodes. However, I also agree that having overlapping relations
containing hundreds to thousands of natural=coastline ways would tax many
data users, and be prone to getting errors from mappers who edit coastlines.
As a sort of compromise at least for bays (gulfs, inlets, fjords, coves),
how about we just map them as a single way across the mouth of the bay and
not as a way-polygon nor type=multipolygon relation? And then we set the
direction of the way such that the right-hand side of the way points to the
bay-side (just like the right-hand side of natural=coastline ways point to
the seaward side).
I know that some people would not like this at all because this is mapping
an arbitrary and fuzzy water boundary. But this avoids creating overlapping
relations and reduces the technical problem to just maintaining a single
way per bay. And for map users and renderers that care about the polygonal
extent of bays, either for labeling purposes or other applications (like
calculating approximate areas), constructing the approximate polygon for
the bay is an easier GIS operation (just concatenate that single way with
the adjacent bay-side coastline ways) than trying to guess that polygon
from a possibly poorly placed node.
If people think this is a good idea, we can even extend this to straits:
just map the ends of the strait with two such ways and combine them into a
relation and tag that relation with natural=strait. (At least this relation
will just contain 2 or a few simple ways instead of also including many
coastline ways.) I guess we would also need to have a new type=* for these
relations, perhaps type=water_extent or something else?
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