I've (finally!) started on the actual modRana vector map rendering support. The plan is to have a pipeline like this:

• vector geometry data source
• filtering
• styling
• rendering

The idea is to have the individual stages more or less independent so that different implementations can be swapped out. Also in some cases multiple stages could be covered by a single implementation (this could be the case for Mapnik - it looks like it should be able to cover styling + rendering and maybe even geometry filtering).

At the moment I'm about done with investigating various existing vector data formats. So far none of them seems to be really suitable for what we need - they are often quite undocumented, don't have fast geographic area access (eq. you can't quickly get data for a given geographic area) or require complex dependencies to generate and/read them.

Therefore I'd probably just settle for a semi-custom vector data storage format based on the time-proven modRana sqlite tile database format. Just instead of the png/jpg blobs stored for the individual tiles there will be (optionally compressed) OSM data for the given tile.

Once I have a working data source (which should be hopefully quite soon), I'd like to start investigating rendering backends, including Mapnik.