On Fri, Sep 7, 2018 at 5:16 PM François Lacombe <fl.infosrese...@gmail.com> wrote: > Le ven. 7 sept. 2018 à 21:40, Richard <ricoz....@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 your idea. '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. _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging