[Tagging] Bridges and layers

[Richard Mann]

On Mon, Jul 26, 2010 at 2:22 PM, Colin Smale <colin.smale at xs4all.nl> wrote:
>  Shouldn't the layer_change be on the common point, not a way? A way
> (usually) has two ends, so putting the tag on a way will not indicate at
> which end of the way the layer change takes place. But then it degenerates
> to two (or more) connected ways with a different layer=* value, so the layer
> change can also easily be inferred without introducing a new tag.

It's more complicated to do it on the joining node, because the node
features on both ways, so you have to know information from the other
way to know how to render. "Can easily be inferred" - only if you have
nothing better to do.

>
> Am I right in assuming that "bridge=yes" refers more to the construction
> (with parapets etc) to determine the rendering style, whereas "layer=*" is
> more a hint to the renderer for handling the case where unconnected objects
> overlap? This is sounding a bit like "tagging for the renderer" which is
> AFAIK officially Frowned Upon. Maybe the real problem is the fact that
> mapnik is not layer-aware.

Falsifying for the renderer is frowned upon. Tagging for the renderer
is reasonable within bounds. See

http://wiki.openstreetmap.org/wiki/Tagging_for_the_renderer

Richard