Javbw
> On May 29, 2019, at 10:37 AM, Joseph Eisenberg <joseph.eisenb...@gmail.com> > wrote: > > What, then, should be the distinguishing characteristic between > waterway=canal and waterway=ditch or =drain? Width or importance or > navigability, or should we still mention the usage as the main > difference? The biggest issue - by far - is conflating construction with purpose. This makes the tags ambiguous. We can invent a definition, but the ambiguity will remain because of our tag value choices, as we have to be careful to manage "purpose". Canal implies construction and purposes. (Many varying purposes). Drain implies a purpose Ditch implies construction. Canals move things from place to place. aquaducts usually exist to move water from one large water body (a lake or river) to another (a holding lake or another river). They are very large (no less than 1 meter, perhaps, usually more) Drains take away waste. We have added "construction" to the definition: "they are lined - concrete or steel or whatever" Ditches are dug into existing ground. In some places, irrigation is separate from storm water management. A storm drain takes wastewater to a river. An irrigation ditch moves water from a supply to a field for orange trees to soak it up. These simple definions work well enough for Southern Califorina. But the Purpose becomes muddied in some places when they are linked together. Here in Japan, we probably have 4x the length of drains than roads. It is immense. They are in every street and and every rural area. They channel rainwater across the land for farming. The "storm drain" system is the irrigation system. One Field's runnoff is the next Field's supply. Drains run from small weirs in streams and canals. These cast concrete drains surround each group of fields. The drains feed ditches which flood the fields and *go back* into the same drains which *feed* the next set of ditches. They are cross connected everywhere, like a spiderweb. Farmers turn them off with large sluices, little sliding gates, and dirt mounds to control how and when fields flood. They have thousands of tiny resivoirs the size of a backyard pool scattered everywhere. The help collect rain and balance distribution load for irrigation. Irrigation canals - aquaducts - are quite rare. Every town has one or two. They move water from one water body to the next, balancing the supply in an area (the California aquaduct is huge and manages the supply for California), but only one aquaduct I Know of is larger than 1 meter). Drains collect and/or distribute water in man-made structures to/from larger ones (rivers, streams, lakes etc) Ditches collect and/or distribute water in ditches carved into the ground, with little to no improvement. Adding purpose via an additional tag (like canal does) is the only way to make sense of it. (and "both waste and irrigation" must be an option). Javbw _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging
