[OSM-talk] Layer transitions

[Richard Mann]

On Sat, Aug 8, 2009 at 1:20 AM, Roy Wallace <waldo000000 at gmail.com> wrote:

> In other words, at any node which is a junction of way
> segments with different layers (whether the segments are part of the
> same way or different ways), the physical implication is that the
> slope of the way changes in the close vicinity of that node. I think
> this would then allow for layer transitions at T-junctions.
>
You can only get away with this if all of the arms of the junction render
the same (yes it is tagging for the renderer; that is only bad if you
falsify to achieve a rendering effect). Highway T-junctions are
significantly more likely to have undesirable rendering effects, so it's a
good idea to have all arms at the same layer. Nodes with only two ways (an
I-junction?) and waterway T-junctions are much less likely to cause
rendering problems if the layers are different. If you want to infer that
the layer changes in the vicinity of the layer-change node, feel free, but
it's probably safer to infer that it gradually changes along the length of
the way that is layer<>0.

Richard
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