I would like to superimpose openstreetmap data over a raster image, using mapnik. My problem is that this image is not in a projection being defined by a SRS, I have some non-linear algorithm to run to be able to match a pixel and a geographic position. Another possibility would be to modify every longitude/latitude in the database to set them to the corresponding pixels, but I'm afraid that it won't play well with the internal reprojections in mapnik. I still have the possibility to do everything by hand using the OSM API, but the result would be ugly. I finally did it by hand. The hardest part was finding non outdated informations about OSM and the library ecosystem. The generate_tiles.py script only works for mercator. For a more flexible tiling system that supports Mapnik and any projection see MapProxy and for extra details see the mapnik-users thread on this type of setup: https://groups.google.com/forum/#!msg/mapnik/YBqjwv4YU0w/TVD0KqYxeG4J Source.