W dniu 16.11.2018 o 14:31, Christoph Hormann pisze: > Quoting from:
Thanks, that was really helpful answer. The problem is that I have asked you how to draw verifiable node, not "what is a good practice for drawing a node using verifiable operations". Let's look closer: > in the middle between the coasts of the strait at the > narrowest point" The hidden prerequisite here is to know which part of the coast belongs to the strait and which is not. But when you know it, it's also easy to define equally (also not fully) verifiable area: "take the coast that belongs to the strait and link the ends with lines without crossing them" > approximately at > the middle of the bay with equal distance to the coast enclosing the > bay on all sides." When you claim that you don't know which part of the coastline belongs to the bay, how do you measure a middle of that? > "If you want to formulate a formal mathematical rule for where the node > for a bay is best placed: Place it so the variance of the distance of > the node to the bay's shores is minimized. Most existing nodes comply > with this rule remarkably well." Again - distance "to the bay's shores", so first you know which parts of the shore belong to the bay (you don't take the whole continent for sure) and then do some strict operation with it (but chosen by some convention). So we claim that we don't know the bay borders, but we derive a node from them. When somebody will claim that the coastline around the bay is different (longer, shorter, has different starting and ending nodes etc.), the node would be placed somewhere else. And while you both can agree on the algorithm, the input is different, so most probably the output will be different too. There can be only verification of applying the same procedure, but not the object (or a node) itself. And it can't be. The only fully verifiable water area is the one fully surrounded by the land (excluding problems with intermittent waters). Then drawing the coastline is fully accurate, because you might choose different ways to draw a node for it and only one way to draw the area. Any water area that is even partly open (to the sea, river, lake etc.) is not fully (100%) verifiable. But the node is also not verifiable, because you need to start with some assumptions about where it starts or ends for a given object to make some formal operations on it. My preference is to show the borders explicitly, so the user will choose what to do with it (measure the area, show the borders, put a node this or the other way...) and has a mostly realistic picture of the object. Making node is hiding the borders, size and shape as an implicit choice on behalf of all the users. I don't say that nodes should be never used for bays or straits. I just claim that they are less usable than areas, because they loose more data, while being also never fully verifiable. Both are just conventions to describe some place on the water, because there are no clear borders on the water. That is also why the coastline is never fully verifiable, but I would be against solving it by using a node instead of a conventional straight line - visible for example on La Plata estuary up to z7: https://www.openstreetmap.org/query?lat=-36.29153&lon=-56.77843#map=7/-35.782/-55.684 -- "Excuse me, I have some growing up to do" [P. Gabriel] _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging
