[OSM-talk] How do bridges work?

[Rick Collins]

At 09:00 AM 10/17/2007, you wrote:
>In message <E1Ii8I4-0002tE-Sp at streetmap.vm.bytemark.co.uk>
>         Rick Collins <gnuarm.2006 at arius.com> wrote:
>
> > Yesterday when I was viewing this section, I could actually see lines
> > drawn to indicate the ends of the bridges.  Now I see nothing like
> > that and even the bridges that look ok can't be distinguished from
> > intersections.
>
>Only the tiles at home layer draws the bridge symbols - the mapnik layer
>just draws the roads crossing (but stacked correctly where you can
>tell the difference).

But should the roads look like intersections?  There is a thin grey 
border at road edges and this line disappears where roads 
intersect.  These "bridges" look the same way with the grey border 
missing at the points of intersection.


> > I used a "bridge" = "yes" tag on all of the sections that should be
> > passing on top.  They were not displaying correctly so yesterday I
> > added a "layer" = "+1" tag to each of them.  This looks worse now
> > than it did before I changed it.
> >
> > Am I still doing it wrong?  How do I get bridges to display correctly?
>
>Add bridge=yes (only use by tiles at home currently) and use layer
>tags to indicate the correct relative ordering of the roads. So
>normally the road on the bridge is layer=1. Complex interchanges
>may need layer=2 etc to get everything stacked right.

So what could be making the bridges display incorrectly?  Even the 
few that are close to "right" don't seem correct to me.

One such bridge is at 39.4, -77.409.  The primary road, South Market 
St, is the bridge passing over the Interstate highway, I-70.