[Tagging] Bridges and layers

[Richard Mann]

On Mon, Jul 26, 2010 at 11:37 AM, Pieren <pieren3 at gmail.com> wrote:
> On Mon, Jul 26, 2010 at 11:58 AM, Richard Mann
> <richard.mann.westoxford at googlemail.com> wrote:
>>
>> Good idea, or just a local fix?
>>
>> Richard
>>
>
> Personally, I think the easiest to fix many issues would be to draw a
> specific polygon for the bridge and link it to the roads, cycleways,
> railways, etc by a relation. I don't know for renderers...

Multiple parallel bridges is a different problem, though it's related,
because of the way Mapnik puts heavy in-layer casings for bridges, to
try to make up for the fact that it doesn't do normal casings
in-layer. The halo it uses for cycle tracks doesn't help either.

http://www.openstreetmap.org/?lat=51.7911&lon=-1.29257&zoom=17&layers=M

The reason it doesn't do casings in-layer is because it produces
rendering artefacts, because it doesn't know when the layer changes.
Of course, you could pre-process it, but rather than make everyone do
that, I'm suggesting putting in an explicit tag for the few occasions
when it's not easy to infer.

Richard