To increase one more zoom level in OSM, follow the given steps:-
1. Edit renderd.conf file located at
/usr/local/etc/ and add this-
Now, save the file and close.
2. Edit the file
In line number 37 and 44 set numZoomLevels: 20;
In line number 39 add
map.setCenter (new OpenLayers.lonLat(659688.852138, 5710701.2962197), 20);
3. Re-render the tiles. The zoom level will be increased.