[OSM-dev] Strange Mapnik rendering

[Lennard]

Maarten Deen wrote:
> Is there an explanation why Mapnik renders the unclassified road on top of
> the primary road in this example?
> <http://www.openstreetmap.org/?lat=51.35217&lon=6.01257&zoom=17&layers=B000FTF>

Yes, partly: rendering order is broken in certain situations, mostly 
related to layer=* issues.

> I tried to hint to Mapnik that the unclassified road should not be
> rendered over the primary by adding a layer=-1, but that didn't help. The
> roads are on the same level.

Don't tag for the renderer. If the roads are on the same level, they 
should have the same layer tag. And if they have the same layer tag, 
rendering is partly first-in-first-out, and partly hard to explain 
because of the current obfuscation level in the stylesheet.

Having said that, there could be some basic rules in the renderer. Like 
draw all link roads first, then all lower class roads, followed by 
higher class roads. We'll get there soon enough, but the stylesheet is 
in some major flux right now.


-- 
Lennard