Coarsening the zoom granularity

Can someone tell me where the granularity of the zoom jumps is set in Mapnik? We’re reckoning to build an internal-use tileserver that mostly needs the zoom levels nearest the ground, for use in foot travel. The higher levels (city-at-a-glance and similar) quite likely won’t be needed at all because of a special indexing scheme, or at most will be reduced to 1 or 2 levels for the convenience of dragging. So, if we count up from ground level (the numbers actually go the other way, don’t they?) this application will need (e.g.) levels 1-4, then skip to 7 and finally to 14. Since they take up so much disc space, we’d rather only generate the tiles for those levels we’ll actually use.

Many thanks for any help.

I doubt if that helps at all. Keep to the convention that zoom level 0 is the whole earth: 17 & 18 are the most detailed ones rendered by mapnik.

Each higher zoom level requires 4 tiles for each tile in the level above. Therefore all the tiles for zoom levels 1 to n-1 will consume much less space than level n. See

Most implementations render tiles on demand for higher zoom levels: not just for disk space reasons, but also because of database performance.

It is not necessary to use the Google tiling schema. You can build the zoom layers and resolutions just as you wish and pixel size does not need to be multiplied by two. There are also other coordinate systems than the Web Mercator one (The Google projection). However, it can be difficult to use your custom tiles togeter with other tiles.
I do not know how to build custom tiling schemas with OSM-Mapnik tool chain. The GeoWebCache tiling configuration is described here and MapProxy system here