Unknown child node: Map > Parameters

[cspanring]

I'm actually not sure if this is a TileStache, Mapnik or TileMill issue, but TileStache (1.31.1, Mapnik 2.0.1+dev20120518) threw an error

.../Providers.py", line 262, in renderArea
mapnik.load_map(self.mapnik, str(self.mapfile))
RuntimeError: Unknown child node in 'Map': 'Parameters'

...when I added a recent Mapnik XML created with TileMill with a <Parameters /> element right after the <Map> opening tag. Removing the <Parameters /> solved it.

[migurski]

Sounds like a Mapnik version mismatch. I'm not sure I've ever seen a Parameters right inside of Map, maybe @springmeyer can shed some light on this?

[springmeyer]

The <Parameters/> element (as a subelement of the <Map>) is new in Mapnik 2.1.x, and is basically a container to stash arbitrary key:value pairs (mapnik/mapnik#977). TileMill started leveraging this in 0.9.1. This means that stylesheets written by Mapnik 2.1.x that use this feature will break if loaded by older versions of Mapnik, which is the problem in this case. It is safe to remove them when you hit this - it is not ideal at all that this creates a breakage, so I will give thought to how/where to avoid this.

[migurski]

Thanks Dane!

Can Tilemill be asked to output older versions of the Mapnik XML?

[springmeyer]

No, TileMill cannot be ask to output older Mapnik XML. But the stable Mapnik 2.0.x series can be made to be kinder in situations like this, which I have just done. See mapnik/mapnik#1286.

I don't see any other fix other than recommending users of TileMill and TileStache together run either the upcoming Mapnik 2.0.2 or Mapnik 2.1.x.

[cspanring]

Fixed in recent (>= 2.2) Mapnik versions.