See my response to N7FMH to see why this is not necessarily a good idea.  It has to do with what area coverage is desired for the increasing zoom levels, all of the area originally covered or just the center as if you had manually zoomed the whole way in at a constant screen center.  The client currently does the former on the prefetch which results in a 4x tile count for each zoom closer.  The latter does a constant tile count per level, but doesn't end up fetching detail for ALL of the area originally viewed.

See the table at http://wiki.openstreetmap.org/wiki/Slippy_map_tilenames#Zoom_levels to get an idea of the total tile count for various zooms.  For your suggestion of 15, if you did this while zoomed out to the planet view, you'd end up fetching (left column is zoom tile count, right column is cumulative total).

1	1
2	4	5
3	16	21
4	64	85
5	256	341
6	1024	1365
7	4096	5461
8	16384	21845
9	65536	87381
10	262144	349525
11	1048576	1398101
12	4194304	5592405
13	16777216	22369621
14	67108864	89478485
15	268435456	357913941
16	1073741824	1431655765
17	4294967296	5726623061
18	17179869184	22906492245

Oh, and you'd have to multiply all of those numbers by the number of tiles it takes to fill the screen from which you did the Prefetch.

Lynn (D) - KJ4ERJ

kc9gqr wrote: