On Tue, Aug 4, 2020 at 3:16 PM Frederik Ramm <frede...@remote.org> wrote:
> Hi, > > On 8/4/20 18:28, Kevin Kenny wrote: > > In actual practice, in the estuaries of rivers, the 'coastline' is very > > seldom tagged that far upstream. > > From my Chesapeake Bay example, in OSM, Havre de Grace (290km inland) is > a "coastal"city > > > https://www.openstreetmap.org/?mlat=39.5443&mlon=-76.0961#map=10/39.5443/-76.0961 > > though Baltimore (260km inland) is not, due to Patapsco River having its > own polygon: > > > https://www.openstreetmap.org/?mlat=39.2461&mlon=-76.6523#map=10/39.2461/-76.6523 > > Of course my "xxx km inland" depends on where you define the bay to > begin, I used the US13 crossing at Norfolk. > > Not saying that is the measuring stick, and perhaps as a result of this > discussion it needs to be tagged differently, or maybe the physical > geography is different there. > > Chesapeake Bay is commonly understood (not among biologists or oceanographers, but in everyday speech) to be a marine environment. Even its name suggests that. Moreover, the Susquehanna is where the fall line comes closest to the coast; and so has the least problem of all the Eastern US rivers. Nobody sane would place the 'coastline' above the Conowingo dam, only a few km from Havre de Grace.Were it not for the dam and lock, Conowingo would be the limit of navigability of the Susquehanna, and the Potomac would not be navigable beyond Washington without the C&O Canal infrastructure. In any case, the number of words we've all exchanged on this topic itself indicates that what we're trying to do is to fix indefinite boundaries. Whether a particular land-water border is 'coastline' or not, for most purposes, is a distinction without a difference. You have land on one side, and water (of whatever salinity and tidal variation) on the other. The water likely belongs to one or more water bodies that have names; the boundaries among named water bodies are almost always both indefinite and culturally determined. Rivers are (usually) fresh and (usually) flow in one direction. The ocean is salt and is (usually) tidal. We use 'estuary' to describe the whole indefinite continuum between. For the Hudson, a hydrologist would correctly say that the whole thing from the dam in Troy to the ocean is estuarine. There are no bright lines separating the pieces. Since there are no bright lines, there is a weaker technical argument in favor of making the 'coastline' as small as possible - minimizing the extent over which trivial mapping mistakes cause continent-wide rendering gaffes.
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