[Talk-us] Best practices for coastline to Inland Bay / River transition

Phil! Gold phil_g at pobox.com
Thu Jan 7 20:47:52 UTC 2016

* Elliott Plack <elliott.plack at gmail.com> [2016-01-07 20:12 +0000]:
> What are the current accept[ed] best practices for determining where to "cut
> off" the coastline and to begin a river or bay type feature? The wiki seems
> to be in disagreement about this, and I've read chatter about switching to
> ocean polygons.

I'm not sure I've seen a best practice, really, but I have in the past
closed off rivers at their mouths and then tagged their (multi)polygons
waterway=riverbank, tidal=yes.  (Sometimes it can be difficult to tell
where a river stops being tidal, but at least the Potomac doesn't have
that problem.)

My reasoning is essentially along the same lines as what to do when one
river flows into another: at some point the smaller river ends and you
could do worse than to draw a line across the mouth of that river and say,
"Everything on this side is River A and everything on the other side is
River B".  Likewise, at some point, the ocean stops being the ocean (or
the Chesapeake Bay stops being the Chesapeake Bay), so why not at the
mouth of the river?

Bays are a little more problematic, as there's not always as obvious a
mouth as for a river, plus features like bays and coves can coexist with
other features like rivers.[0]  I usually leave bays as point features
unless there's a really obvious delineation between them and everything

I actually went through the work of cutting the Potomac off from the
coastline of the Chesapeake Bay and turning it into riverbank
multipolygons a few years ago, but JOSM crashed and lost my work before I
was able to upload it and I felt too depressed to go back and redo
everything.  I believe I have since gone back and put in *some* riverbank
multipolygons at the upstream end of the tidal region of the river.

[0] I know according to some points of view, the entire Chesapeake Bay is
    just the lowest part of the Susquehanna River, but I'm pretty
    comfortable leaving the Bay as coastline.

...computer contrarian of the first order... / http://aperiodic.net/phil/
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