On Mon, Apr 21, 2014 at 09:53:21PM +0100, Chris Hill wrote: > On 21/04/14 21:20, Martin Koppenhoefer wrote: > > > >2014-04-21 20:48 GMT+02:00 Richard Z. <ricoz....@gmail.com > ><mailto:ricoz....@gmail.com>>: > > > > > Without any additional tags like "tunnel=*" or "covered=*", a > > > "layer=-1" river shouldn't be rendered differently than a > > "layer=1" or > > > even in the absence of any "layer" tag. This is a bug in OsmAnd. You > > > > except for the the very frequent case when the river with a layer=-1 > > goes through a landuse=* area with a layer=0. > > > > > > > >+1, as soon as there is any other object on a different layer, be > >it landuse, a place area or something else, with the lower layer > >tag you are excluding the river from this feature and putting it > >below. > > Layer is a hint to the renderer. The item with the lowest layer > value is drawn first, then the next highest and so on. In the > example of where a road crosses a railway on a bridge, the railway > (often default layer=0) is drawn, then the road (often layer=1) is > drawn,casing first then inner and any part that crosses the railway > obscures that part of the railway.
we don't have a bridge here. > What you are saying is that the river (layer=-1) is drawn then the > landuse (layer=0) is drawn over it, obscuring the river. This is > clearly not intended and not what actually happens in Mapnik > renders, which is much smarter than that. in other words mapnik is applying artificial intelligence trying to work around obvious errors in OSM data. > Layer tag is a *hint* to the renderer, nothing more. the wiki page says << The layer=* tag is one of several methods used to describe vertical relationships between crossing or overlapping features. >> Not a single word of a "hint to the renderer" anywhere in the article. If the definition of "key:layer" would become "a hint to the renderer" we could clearly abolish it. We don't tag for the renderer means ***we do not need hints for the renderer***. Especially not bad ones. And how much worth is a "hint to the renderer" if the renderer can only work by deliberately ignoring the hint? Now what is that key:layer anyway? Given that nobody knows or cares how it works does it do more good than harm? Do we need it at all? Or should we make a fresh start with something well defined and deprecate this mess? Richard _______________________________________________ Tagging mailing list Tagging@openstreetmap.org https://lists.openstreetmap.org/listinfo/tagging