It's perfectly possible to make a physical definition of an estuary which allows the line of the natural=coastline to be placed across the lower Hudson, rather than at Troy or Albany, if we look at salinity and currents rather than just tides: and we must, because some parts of the coast in the tropics have nearly 0 tidal variation (including the region around the Rio de la Plata).
But the current position of the natural=coastline ways between Argentina and Uruguay is like if all of Lower New York Bay were outside of the natural=coastline, and a line was instead drawn from Long Beach NY to Long Branch NJ. This is quite serious when it comes to the Saint Lawrence river (Fleuve Saint-Laurent), which can extend as far west into the Golf of Saint Lawrence as you want, if we take the current placement of the natural=coastline along the eastern edge of the Rio de la Plata as a guide. I would suggest that the natural=coastline should cross no farther downstream than Quebec City, where the river widens into the huge lower estuary. Similarly, should Puget Sound and San Francisco Bay be mapped as natural=water + water=river? These are also estuaries. -- Joseph Eisenberg On Tue, Aug 4, 2020 at 9:30 AM Kevin Kenny <kevin.b.ke...@gmail.com> wrote: > On Tue, Aug 4, 2020 at 11:24 AM Joseph Eisenberg < > joseph.eisenb...@gmail.com> wrote: > >> This means that the line tagged with natural=coastline is on the inland >> side of all marine water, including mangroves, salt marshes, and tidal >> channels, as far as possible. It makes sense that in estuaries, the route >> of the ways tagged natural=coastline should also extend up to the limit of >> marine influence. In some cases this has been taken to mean the limit of >> the tides, in others it is the limit of mixing of salt and fresh water. >> > > I agree that's what the Wiki says. The Wiki says a lot of things. > > In actual practice, in the estuaries of rivers, the 'coastline' is very > seldom tagged that far upstream. > > I return to the example of the Hudson River. The tidal influence extends > upstream to Lock and Dam Number One - 248 km from the river mouth. The salt > front varies strongly with the season. There can be fresh water in New York > Harbor during the spring snowmelt, or salt water at Poughkeepsie (122 km > upriver) in a dry summer. (It's also defined somewhat arbitrarily as a > conductivity of 510 microsiemens/metre at the surface - but surface > salinity is, in most seasons, higher than the salinity at depth because the > cold, fresh river water underlies the relatively warm, brackish surface > water.) Needless to say, the biome is very different between Albany (always > fresh water) and Yonkers (always salt, except for snowmelt events). > Oceangoing vessels of up to 9 m draft can ply the river as far as Albany. > (In less xenophobic times, vessels of friendly nations could clear customs > at Albany.) > > For pretty much all the rivers in eastern North America, the tidal > influence extends to the first dam or waterfall. This usually coincides > with what would be the head of navigation if it were not for modern > improvements such as locks. Riverports from Augusta, Maine to Macon, > Georgia would become 'coastal' cities. That's surely no more the local > understanding on the Kennebec or the Ocmulgee than it is on the Elbe! > > For the Amazon, the situation is even more extreme - the river is tidal > for a thousand kilometres from what would be conventionally recognized as > the 'coast'. > > It appears that for most of the world, this rule, if actually implemented > - and it is important to stress that it is NOT the way things are mapped at > present - would extend the 'coastline' for tens or hundreds of km upstream > on most of the first-order rivers of the world. > > Given the fact that even with today's definition, we frequently go for > months without a consistent coastline to give to the renderer, do we want > to add tens of thousands more kilometres of 'natural=coastline'? We'd never > see a coastline update again! (For this reason, I'm inclined to push the > 'coastline' as far toward the sea as sensibly possible, to have as little > 'coastline' as possible to get broken, rather than going for months without > updates or worse, seeing rendering accidents flood whole continents.) > > Moreover, I'm somewhat puzzled at Christoph's insistence that > 'natural=coastline' have a strict physical definition, and dismiss local > understanding as merely political and cultural. In almost all other aspects > of OSM, the understanding of the locals is what governs. That understanding > is, ipso facto, cultural - but we dismiss it at our peril. Ignoring local > understanding is a path to irrelevance. (In another OSM domain, I've seen > this sort of nonsense before; I've actually seen someone seriously suggest > that a peak should not have its name in OSM unless someone can find a sign > with the name on it, because asking locals and consulting reference works > is not 'verifiability in the field.') > > -- > 73 de ke9tv/2, Kevin > _______________________________________________ > Tagging mailing list > Tagging@openstreetmap.org > https://lists.openstreetmap.org/listinfo/tagging >
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