On Wed, Feb 05, 2020 at 05:28:03PM +0100, Christoph Hormann wrote: > On Wednesday 05 February 2020, Jeroen Hoek wrote: > > > the semantic ambiguity of the > 350k cases where barrier tags are > > > currently used as a secondary tag on landuse/leisure/etc. polygons > > > to incidate the polygon is enclosed by a linear barrier. > > > > The PR specifically removes the filled rendering from `barrier=hedge` > > mapped with `area=yes` from 36665 hedges. > > No, it does not, the PR removes the fill rendering of all *polygons* > tagged barrier=hedge. This includes closed ways with barrier=hedge and > area=yes, closed ways with barrier=hedge and a different tag implying a > polygon and also multipolygons. I explained the way the renderer > interprets the data in the PR discussion. Understanding this and > understanding the current meaning of the area=yes tag is *essential* > for understanding the reasoning behind this change.
area=yes is a secondary tag that has the meaning "the way it is on is an area, no matter what any other tag suggests". So clearly, if something is tagged barrier=hedge+area=yes, it must be a hedge mapped as an area. Our current interpretation of the tag leaves no room for interpretation here. The more interesting case is barrier+landuse. You argue that the presence of landuse makes the entire OSM way a polygon. I know that osm2pgsql implements it this way but I don't think that is entirely correct. barrier and landuse are two main tags. The rules what happens, when an OSM object has two main tags are a bit on the fuzzy side. In general we have interpreted it as a short cut for: there are essentially two objects that share the geometry and the secondary tags. That does not mean that one main tag inherites all the implicit assumptions of the other main tag. So in this case a barrier does not automatically inherit the implicit area=yes of the landuse tag. In this interpretation the landuse inherently is a polygon, the barrier inherently a line feature. > What you essentially want is for barrier=hedge on polygons to have a > different meaning depending on the presence of area=yes. Given the > very specific and highly significant technical meaning of area=* > overloading it with additional more specialized meanings w.r.t. > specific tags seems a very bad idea to me. I don't understand what the special case here is. area=yes makes a feature a polygon. Always. It doesn't matter what the main tag is. It just means that the object has been mapped in two dimensions instead of the usual one. > I never claimed it to be. What i did say is that what is mapped with > barrier=hedge on polygons with a different meaning than 'this polygon > is enclosed by a hedge' is elsewhere predominantly mapped with > natural=scrub/wood or landuse=forest. I demonstrated this with links > to various places. No, the meaning of a barrier=hedge on a closed way without area=yes is exactly the same as for a barrier on a non-closed way: there is a hedge that follows the path of the line. The fact that the line meets at its ends is not relevant for the interpretation. Sarah _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging
