[OSM-dev] OT: generate_tiles.py generates blank images

[John McKerrell]

Hi

First off, I'm afraid this isn't actually OSM related, but I'm hoping  
you'll help me out anyway.

I'm trying to generate some tiles for postcode boundaries of a single  
UK city using mapnik. I've successfully generated a single image but  
when I try passing the same XML file into generate_tiles.py I just get  
blank data back. Does anyone have any suggestions for why? I'm pretty  
sure I'm passing the right bb in, it's (minlon,minlat,maxlon,maxlat)  
right? Here's what I'm using for swansea:

	bbox = (-4.09104,51.55263,-3.84899,51.67649)

Any help would be much appreciated, am trying to avoid going with  
modtile for now as I'm generating the tiles for a client and can't  
control the servers they'd be hosted on, and I haven't setup modtile  
before.

Cheers,

John