How do you know the direction of water flow if you don't have the way? Janko
uto, 14. tra 2015. 11:45 Torstein Ingebrigtsen Bø <torstein...@gmail.com> je napisao: > Hi, > > I'm currently importing topological data of Norway to OSM. From the data > set we have riverbanks; however, we do not have the deepest middle way as > required by the wiki [1]. This middle line is therefore drawn manually. > This is a time consuming (and dull) job. For one municipal it takes around > 5-10 hours to draw all these lines, in Norway we have 428 municipals. > Drawing all these middle lines will slow down the time to import everything > dramatical. I am therefore curious of what is the benefits of this line. Is > it really necessary or is it a "nice to have"? > > Some disadvantages with this middle way are: > - The line add redundancy. I guess that many add this line such that it is > inside the multipolygon of the riverbank. Doing so the added data is only > the direction of the river. (Other tags may be added to the multipolygon.) > - Sometimes people draw the line wrong or forget to update it when > updating the multipolygon. I have seen "middle" lines outside of the > multipolygon (either inside islands or outside of the multipolygon). This > gives false islands and splitting of islands when rendered. > - A similar way can be generated, if direction and deepest point is not > required. This comes as a fact of the first point and removes the > previously mentioned problem. > - For routing purposes this is not needed. (I have not seen any practical > marine navigation/routing implementations yet, either.) Routing algorithms > may also represent a riverbank as a node (or multiple nodes). The same > problem occurs for lakes where it is not required to have a middle way for > routing. > - The direction of the river is seldom used. The direction of a river is > seldom (or never?) rendered in any map. It is implicitly shown (e.g., by > contour lines). > - Specifically for the import of Kartverket N50 [2], this requirement is > slowing down the import process dramatical and import of other data of more > current value are delayed. This is therefore also a question of > prioritizing data to be imported. > > I therefore propose to make this middle way in riverbanks recommended > (when the deepest way is known), not required. > > [1] http://wiki.openstreetmap.org/wiki/Tag:waterway%3Driverbank > <http://wiki.openstreetmap.org/wiki/Tag:waterway%3Driverbank#Old_tagging> > [2] > https://wiki.openstreetmap.org/wiki/Import/Catalogue/N50_import_(Norway) > > Best regards, > Torstein I. Bø > tibnor > _______________________________________________ > Tagging mailing list > Tagging@openstreetmap.org > https://lists.openstreetmap.org/listinfo/tagging >
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