[Tagging] coastline v. water

Sarah Hoffmann lonvia at denofr.de
Sun Nov 22 08:33:29 UTC 2020


On Sat, Nov 21, 2020 at 07:09:45PM +0000, Eric H. Christensen via Tagging wrote:
> You cannot point to other area that may, in fact, be improperly mapped as an example when they are like that because locals have been shouted down for doing it correctly. The fact that this keeps coming back up literally means that there is not universal agreement that "marginal seas", whatever that means, are to be mapped with natural=coastline.
> The Chesapeake Bay is an estuary that, by definition, opens to the sea. It can't be a sea and open to a sea at the same time. In this environment, it is different from the ocean in which it opens into and is also different from the tributaries that feed it. These are protected waters for ships. You won't find any high seas forecasts for the Bay unlike the ocean. The Bay is also brackish and not defined as salt water, unlike the ocean.

There is a very fundamental misunderstanding on how OpenStreetMap works
in here. The definition of a tag comes from the agreed-on understanding
of the OpenStreetMap community as a whole of what that tag should be. This
may or may not agree with defintion of the same word in other contexts.
That's just the way it is with defintions. They may differ. You cannot just
uniterally apply a definition of coastline that you think is more
appropriate, or scientifically correct or whatever and change the map.
It is OSM's definition that counts, and OSM's defintion only.

That doesn't mean that definitions can't evolve over time but that needs
to be discussed when it has a larger impact. natural=coastline
is a particular touchy tag here because it is one of the few tags where
we rely on a agreed-on definition that works on a planet-scale. Even if
you change something relatively locally, it has an effect on how the
planet map as a whole is rendered. You can't just apply a new definition
to one bay. We must agree on a new definition globally here and apply it
globally or the tagging becomes a worthless mess.

So please, by all means, start a discussion about a new definition of
coastline, make a wiki page, put it up for voting. But all this should
be done **before** making any larger changes. For now, please, put
the Chesapeake Bay back into its original state.

Kind regards


> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Saturday, November 21, 2020 1:14 PM, Joseph Eisenberg <joseph.eisenberg at gmail.com> wrote:
> > Eric,
> > I don't think the previous discussion is quite as inconclusive as your evaluation.
> >
> > 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: https://www.openstreetmap.de/karte.html?zoom=10&lat=39.14649&lon=-75.07302&layers=B000 - it is mapped as a natural=bay with natural=coastline around it, not natural=water
> >
> > 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) - https://www.openstreetmap.de/karte.html?zoom=10&lat=40.63628&lon=-73.93525&layers=B000
> >
> > Tampa Bay: https://www.openstreetmap.de/karte.html?zoom=10&lat=27.80801&lon=-82.63368&layers=B000 - outside of the natural=coastline
> >
> > Galveston Bay: https://www.openstreetmap.de/karte.html?zoom=10&lat=29.49869&lon=-94.94249&layers=B000TT - outside of the natural=coastline
> >
> > San Francisco Bay and connected bays: https://www.openstreetmap.de/karte.html?zoom=10&lat=37.79939&lon=-122.06911&layers=B000TT - 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: https://www.openstreetmap.de/karte.html?zoom=11&lat=47.59544&lon=-122.39252&layers=B000
> >
> > 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 natural=coastline.
> >
> > 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 https://wiki.openstreetmap.org/wiki/Tag:waterway%3Dtidal_channel#How_to_Map and https://wiki.openstreetmap.org/wiki/Proposed_features/Tag:waterway%3Dtidal_channel - 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
> >>
> >> _______________________________________________
> >> Tagging mailing list
> >> Tagging at openstreetmap.org
> >> https://lists.openstreetmap.org/listinfo/tagging

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