Mapnik layer

routes-bg.xml

    <Style name="routes-bg">
        <Rule>
            &maxscale_zoom17;
            &minscale_zoom18;
            <LineSymbolizer stroke-width="18" stroke="#FFFFFF"/>
        </Rule>
    
        <Rule>
            &maxscale_zoom16;
            &minscale_zoom16;
            <LineSymbolizer stroke-width="10" stroke="#FFFFFF"/>
        </Rule>

        <Rule>
            &maxscale_zoom14;
            &minscale_zoom15;
            <LineSymbolizer stroke-width="7" stroke="#FFFFFF"/>
        </Rule>
        
        <Rule>
            &maxscale_zoom12;
            &minscale_zoom13;
            <LineSymbolizer stroke-width="4" stroke="#FFFFFF"/>
        </Rule>
        
        <Rule>
            &maxscale_zoom9;
            &minscale_zoom11;
            <LineSymbolizer stroke-width="2" stroke="#FFFFFF"/>
        </Rule>
    </Style>
    <Layer name="routes-bg" srs="+proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +no_defs +over">
        <StyleName>routes-bg</StyleName>
        <Datasource>
        &datasource-settings;
            <Parameter name="table">
            (select * from planet_osm_line where "piste:type"='nordic' and route IS NOT NULL and color is not null order by z_order) as pistes
            </Parameter>
        </Datasource>
    </Layer>