[Tagging] Water in bays, harbors, etc.

Kevin Kenny kevin.b.kenny+osm at gmail.com
Tue Sep 6 18:34:05 UTC 2016

I'll be following this discussion with interest, because I suspect that a
good many mappers have the same approach that I do in estuarine areas:
"don't mess with the coastline, you're too likely to break something."

My understanding is that the coastline is *supposed* to follow the
high-water line of the mean spring tide of a 19-year Metonic cycle. In the
field, though, what I see mapped is something closer to mean daily high
water, or even lower, because otherwise most of the renderers would place
the entire foreshore under water. Moreover, the coastline often seems to
follow the barrier islands, with the back bays, estuaries, and other
waterways not accounted as part of the ocean, even if the water is salt.
There will always be confusion in that area. It would surely be wrong to
label the Hudson River as merely an arm of the Atlantic Ocean, even if the
water is brackish for fifty kilometers or more upriver, and the tide is
measurable for another hundred km beyond that, so there has to be some room
for judgment.

If the natural=coastline followed the mean high water of the Metonic cycle,
as documented in http://wiki.openstreetmap.org/wiki/Tag:natural%3Dcoastline,
many of the residential areas in a waterfront community like my native area
of http://www.openstreetmap.org/#map=15/40.6160/-73.7555 [1] would render
as being underwater - they routinely have water in the streets for an hour
or two at the spring tide, particularly if the wind is offshore.
Technically, they are indeed 'outside' the coastline, but practically, that
description does not make sense. All the buildings are on piers, typically
a couple of metres above grade, and people don't think of themselves as
living under water. They just keep an almanac close at hand to know when
the road will be flooded.

73 de ke9tv/2, Kevin

[1] People often ask, "why would people build in an area that's so very
subject to flooding?" The answer is simple: "because it's hard to put a
seaport anywhere but on the ocean."  And now I see that I have another
thing on my ever-growing list of projects. I see a couple of streets on the
map there that have been abandoned since the hurricane of 1960 and have
been underwater since the 1970s at the very least. They are no doubt 'TIGER

On Sun, Aug 21, 2016 at 11:48 AM, Tod Fitch <tod at fitchdesign.com> wrote:

> During a day kayaking I noticed that the OSM map in the area was less than
> perfect so I thought I’d see what I could do to improve it. But I have not
> worked on this type of feature very much and am a little uncertain of some
> tagging details.
> The area is a “back bay”, a tidal area with some channels and tidal
> wetlands a bit inland from a developed small boat harbor. In this area the
> land/water boundary has been tagged with “natural=coastline”[1]. When
> looking at other similar areas I’ve been to, it seems that the
> “natural=coastline” is not taken as far inland and the harbor and estuary
> areas are tagged with "natural=water”[2]. I am wondering which is the
> preferred method of tagging.
> Thanks!
> [1] http://www.openstreetmap.org/#map=16/33.6201/-117.8968
> [2] http://www.openstreetmap.org/#map=16/36.8100/-121.7859
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> Tagging at openstreetmap.org
> https://lists.openstreetmap.org/listinfo/tagging
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