[OSM-dev] Blank Tiles at z23 and Deeper

[jpk]

Hello all,

Some background:

I recently set up a tile server per the documentation at
switch2osm.org.  (Which is great, by the way.  Many thanks to those
that put that together!)  I built the machine according to the manual
instructions for Ubuntu 12.04.  My application (indoor map making)
requires zooming very deep; currently experimenting around z25 to z30.
 I realize most tiles aren't terribly interesting at these zoom
levels, but I just want tiles to be there for few reasons: maintaining
outdoor context (nearby roads, parking lots, etc), to see edges of
building footprints, and just generally provide a backdrop for stuff
going on on top of them.  In any case, I set up my tile server for
this purpose.  I changed the #define MAX_ZOOM to 30 in mod_tile's
render_config.h, and set MAXZOOM in renderd.conf to 30.  That's enough
to get the tile server to serve tiles down to z30 instead of 404'ing.

However, here's my problem:

All tiles at z23 and greater are solid green-ish (#b5d0d0, to be
exact).  Poking through the mapnik style, I see this color is used as
the background color for the Map element (osm.xml, line 6).  Changing
that color changes the color I see for these solid tiles.  I'm not yet
knowledgeable when it comes to mapnik but in trying to digest the
style files, nothing struck me as explicitly causing this behavior at
>z22.  Additionally, I tried MapQuest's style (found here:
https://github.com/MapQuest/MapQuest-Mapnik-Style) and found the same
thing (except instead of solid #b5d0d0, you get their wavy light-blue
water texture).  Is this a style issue?  A mapnik issue?  renderd or
mod_tile?

There are enough moving parts I'm still learning about that I don't
know where to begin debugging.  If those of you who know your way
around could get me pointed in the right direction, I'd be most
grateful!

Thanks!
jpk

-- 
john p. kiffmeyer