[Tagging] Is waterway=riverbank an 'Old scheme' ?
kevin.b.kenny at gmail.com
Fri Sep 7 22:38:34 UTC 2018
On Fri, Sep 7, 2018 at 5:16 PM François Lacombe
<fl.infosreseaux at gmail.com> wrote:
> Le ven. 7 sept. 2018 à 21:40, Richard <ricoz.osm at gmail.com> a écrit :
>> > The idea that waterway=* must be routable is, frankly, a new one to
>> > me.
>> that idea is nonsense.. there was never the assertion that waterway=ditch,stream
>> be navigable.
> That escalated quickly !
> Routable doesn't mean navigable at all. Hydrographic routable network is about where the water goes.
> Ditches, canals and river where the same property to carry water somewhere.
> You're so focused on particular usage that anything else is non-sense. This is really questionable.
> We'd really better to separate concepts in different keys between water ways and other features like dams, fuel places or piers which doesn't carry water at all.
OK. you're asking that 'waterway' be synonymous with 'flowline' -
that's more likely to be observable, but still not something that
we've had a convention for.
We're gradually and indirectly approaching having a 'routable'
hydrography, in your sense. JOSM, for instance, warns if a
waterway=stream or waterway=river is disconnected at its downstream
end. I doubt that we'll ever get to the point where all waterway=*
tags represent flowlines, but one can get a long way by restricting to
'waterway=river' and 'waterway=stream' (note that a waterway=river is
supposed to be kept continuous by following some approximation to the
Thalweg through lakes, ponds, reservoirs). I don't think we yet have a
convention for 'connector' waterways representing the machinery inside
a dam or the unknown path that water is taking through karst terrain.
I think we could, with some effort, come up with a SUBSET of
waterway=* tags that are expected to be topologically consistent. The
use of 'waterway=riverbank', 'waterway=dam', and so on are rather too
well established to undo at this late date.
Not all ditches and canals have a well-defined direction of flow. I'm
not sure what approach the hydrographers would take to the stretch of
the modern Erie Canal between locks 20 and 21, where it's higher than
the adjacent reaches in both directions (the 'downstream' end drains
eastward toward the Mohawk River, and the 'upstream' end joins Fish
Creek, which flows west into Oneida Lake. I presume, also, that
hydrographers have recognized conventions for dealing with nearly flat
regions where the water doesn't know *which* way it wants to go. The
Preston Ponds in the Adirondacks, for instance, have distributaries in
both the Hudson and Saint Lawrence basins.
I think that if we recognize that not all waterways are flowlines, but
that some waterway=* are expected to be, we can make progress with
'Routable', in this group, often denotes 'usable by a routing engine
to inform a human of a path to take' - and it's imaginable that
someone might want to design a routing engine for watercraft - that's
why we got confused. Routing in terms of 'finding a way that a
watercraft can take' does indeed imply navigability!
I sometimes generate incomplete hydrographic networks, simply because
I'm drawing stuff that I need for a specific map, and don't bother to
trace everything downstream to a watercourse that's already present in
OSM. That's the sort of thing that is at least correct, if not useful
for hydrography, and another mapper can complete it without needing to
undo anything that was already done. Many of these watercourses are
small streams that I cannot follow through urban areas because I have
no idea where the man-made drainage network takes them.
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