[Tagging] Rio de la Plata edit war

Kevin Kenny kevin.b.kenny at gmail.com
Tue Aug 4 16:28:26 UTC 2020

On Tue, Aug 4, 2020 at 11:24 AM Joseph Eisenberg <joseph.eisenberg at gmail.com>

> 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

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
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