[Tagging] layer=-1, rivers, bridges and tunnels

Richard Z. ricoz.osm at gmail.com
Sun Mar 16 00:42:24 UTC 2014

On Sat, Mar 15, 2014 at 03:19:36PM -0300, Fernando Trebien wrote:

> Situation 1 happens in many other cities across the world, and if you
> tag the bridge as layer=1, you may end up inverting the rendering
> order of highways, leading to this:
> http://www.openstreetmap.org/way/138032009

what exactly is the problem here? Colour artefacts on the Quai des Gevres?
If it is affected by the layer than it is a bug in Mapnik - and no, we 
should not use layer to fix bugs in Mapnik.

Looking at the data in JOSM I see a few problems - for example there 
is no reason why this particular way should have any layer tag at all.
It seems completely useless and one of the reasons I want to enforce
the "no layer tag without a bridge/tunnel" rule which would catch
similar accidents.

While not wrong in this case it is also not needed to have the bridge 
at layer=2.

Also building=bridge is the wrong tag for this bridge (tagging for 
Mapnik again ?) but if it is used at all the ways entering the bridge 
ought at least share a node with the bridge where they are entering it.


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