[Tagging] coastline v. water

Joseph Eisenberg joseph.eisenberg at gmail.com
Sat Nov 21 18:14:49 UTC 2020

I don't think the previous discussion is quite as inconclusive as your

While it is true that there is not widespread agreement on where the
natural=coatline ways should transect a river mouth or river estuary, there
is nearly universal agreement that marginal seas, including bays, are
mapped with the natural=coastline.

Using the rendering at https://www.openstreetmap.de/karte.html - which
differentiates the marine water polygons outside of the coastline from
lakes and rivers, by using slightly different colors, we can see how bays
are mapped in other parts of North America and the world.

For example, check out Delaware Bay, just up the coast from your area:
it is mapped as a natural=bay with natural=coastline around it, not

Upper and Lower New York Bay are mapped as bays outside of the
natural=coastline - you can see the line where the waterway=riverbank area
starts just at the north end of Manhattan island (though this placement is
somewhat controversial) -

Tampa Bay:
- outside of the natural=coastline

Galveston Bay:
- outside of the natural=coastline

San Francisco Bay and connected bays:
- outside of the coastline

Puget Sound - while Lake Washington on the east side of Seattle is
natural=water, also most of the ship canal connecting them:

I would like to request that the tidal channels and estuaries around
Chesapeake Bay be re-mapped with natural=coastline. If you wish to keep the
natural-water polygons for the estuaries that is not a problem.

But it would be contrary to normal practice to map the main body of
Chesapeake Bay as natural=water because it is clearly part of the sea -
there is no barrier between it and the open ocean, since there is an open
channel through US 13 where the tunnel is. While it is an estuary by
hydrological definitions, so are the Baltic Sea and all fjords and Puget
Sound and San Francisco Bay - all of which are mapped as outside of the

Also please consider that the community here approved the proposal for
waterway=tidal_channel which said that the area of tidal channels (aka
tidal creeks) should be mapped with natural=coastline at their edges - see
- most of the "creek" features along the Bay are tidal channels.

-- Joseph Eisenberg

On Thu, Nov 19, 2020 at 6:46 AM Eric H. Christensen via Tagging <
tagging at openstreetmap.org> wrote:

> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Wednesday, November 18th, 2020 at 11:34 PM, Brian M. Sperlongano <
> zelonewolf at gmail.com> wrote:
> > This was fascinating reading.  I do agree that we ought to have a
> definition for what gets tagged natural=coastline, and I think it's fine if
> that definition has some subjectivity.
> >
> > I would offer something as simple as:
> >
> > "The coastline should follow the mean high tide line.  In some cases
> this rule would result in the coastline extending an unreasonable distance
> along the banks of tidal rivers.  In those cases, mappers should identify a
> reasonable choke point at which to terminate the inland extent of coastline
> tagging."
> I would just classify it as "where the ocean meets the land".  Any other
> water that isn't ocean should be mapped as water and tagged appropriately.
> That makes the map more accurate and detailed.
> R,
> Eric
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