Re: [Tagging] SF Muni tram lines are layer=1? and general tagging levels considerations

[A.Pirard.Papou]

On 2012-12-17 07:50, Clay Smalley wrote : I noticed the majority of the trackage of the San Francisco Muni lines are tagged as layer=1, while the streets along which they run have no layer tag (an implied layer=0). If the Muni lines are layer=1, it is my understanding that the Muni lines should be physically above the street. Since this is not the case and the lines run at street level, should I remove the layer tag on these specific tracks (to imply layer=0)? (Of course, some of these lines run through tunnels where they are tagged layer=-1, and on bridges where they are tagged layer=1 correctly. The layer tag on these bits of track would remain untouched.) -- Clay A level is an altitude.  A layer is a drawing opacity.  Although OSM does not tag for the renderer, it uses the tag layer=*. It defines layer as the relative "position" (is that "altitude"?). In fact, the only effect of assigning a layer is that upper layer objects hide lower layer ones (it's not a "mind your step" warning ;-)) It's interesting to keep all the rails in the same layer to avoid splits and layer =+1 may be needed for them to show at some places. My reaction would be that the person having cared to explicitly set the level might have had something on his mind. A bridge is a piece of concrete that is under -- relative altitude -1 -- an uninterrupted foil of macadam. It shows just out of each side of the road, like rails and the macadam hides it (that's, to me, how the maps render it too). It can be tagged using a short additional segment overunderlaying the road. Yet, the instructions and practice are to put it at layer +1 and to unnecessarily split and even interrupt the road. Strange. You say that trams run at altitude -1 in a tunnel.  As I see it, a tunnel is layer=+1 even if the tram goes down (underground level) to pass under it. Very complicated. I have traced lengths of streams stream as a constant layer=-2 way, uninterrupted end to end (even if they "don't look so deep"), roads are at level 0 and bridges and culverts at level -1, in the manner mentioned above. If the stream comes to a pond, it continues to flow in a way drawn across the pond, at the bottom of it, just what happens if the pond depletes, all in a very uninterrupted stream way. Very neat, uniform, consistent and simple. Fortunately, streams are always one-way, have no speed limits, etc... and it's easy to keep them in a single thread. It would be possible for roads too with my SEGMENT idea but my e-mail wasn't replied. Roads are even split unnaturally and unnecessarily by bridges. Cheers, André.

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