Well, I say this because I've yet to come across any renderer that doesn't automatically assume layer=-1 for tunnel or layer=1 for bridge when it's omitted.
On Mon, Dec 17, 2012 at 9:24 AM, Martin Koppenhoefer <dieterdre...@gmail.com > wrote: > 2012/12/17 Paul Johnson <ba...@ursamundi.org>: > > On Monday, December 17, 2012, Clay Smalley wrote: > >> > >> (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.) > >> > > > > Though this layer tag is unnecessary if there isn't more than one tunnel > or > > more than one bridge crossing a spot. > > > From a data point of view layer-tags are always necessary when 2 or > more objects cross each other at different levels. For bridges and > tunnels it is good practise to always set a layer tag (and mostly > there will be other objects crossing, because that's the reason why > there is a bridge). In the standard mapnik style there is no need to > set an explicit layer tag though, so for 2 crossing objects one of > which a tunnel or a bridge the rendering will be correct also if the > data isn't complete. > > cheers, > Martin > > _______________________________________________ > Tagging mailing list > Tagging@openstreetmap.org > http://lists.openstreetmap.org/listinfo/tagging >
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