[OSM-talk] Proper use of layer tag with the Mapnik renderer?

[Jon Burgess]

On Sat, 2009-06-20 at 20:02 -0700, Michal Migurski wrote:
> Hello,
> 
> I've just made some edits to this interchange:
> 	http://www.openstreetmap.org/?lat=37.819252&lon=-122.25409&zoom=18&layers=B000FTFT
> 
> I've used the layer tag in what I think is the right way, but the  
> Macarthur Blvd overpass (layer=3, bridge=yes) is now being shown  
> underneath the I580 overpass (layer=2, bridge=yes). Seems like layer  
> should be fairly unambiguous, why wouldn't it be able to draw the  
> overpasses in the correct order? Did I mistag?

The tagging seems reasonable. The current rendering is down to the rules
in the oxm.xml:

<Layer name="bridges" status="on" srs="...">
    <StyleName>road-bridges-casing</StyleName>
    <StyleName>road-bridges-fill</StyleName>
    <StyleName>noncased-ways-bridges</StyleName>
    <StyleName>mwaybridge_layer0_casing</StyleName>
    <StyleName>mwaybridge_layer0_fill</StyleName>
    <StyleName>mwaybridge_layer1_casing</StyleName>
    <StyleName>mwaybridge_layer1_fill</StyleName>
    <StyleName>mwaybridge_layer2_casing</StyleName>
    <StyleName>mwaybridge_layer2_fill</StyleName>
    <StyleName>mwaybridge_layer3_casing</StyleName>
    <StyleName>mwaybridge_layer3_fill</StyleName>
    <StyleName>mwaybridge_layer4_casing</StyleName>
    <StyleName>mwaybridge_layer4_fill</StyleName>
    <StyleName>mwaybridge_layer5_casing</StyleName>
    <StyleName>mwaybridge_layer5_fill</StyleName>
    <StyleName>primarybridge_layer0_casing</StyleName>
    <StyleName>primarybridge_layer0_fill</StyleName>
    <StyleName>primarybridge_layer1_casing</StyleName>
    <StyleName>primarybridge_layer1_fill</StyleName>
    <StyleName>primarybridge_layer2_casing</StyleName>
    <StyleName>primarybridge_layer2_fill</StyleName>


These rules will draw the motorway bridges above any secondary bridges
regardless of the layering. I don't understand the logic behind the
current rules, I believe they were done like this to fix some layering
issues in some other complex junctions.

	Jon


> Here's the same spot from the air for comparison:
> 	http://maps.google.com/?ie=UTF8&ll=37.81923,-122.254277&spn=0.002301,0.004238&t=k&z=18&iwloc=A
> 
> -mike.
> 
> ----------------------------------------------------------------
> michal migurski- mike at stamen.com
>                   415.558.1610