Switch back to minimal footprints

[mojodna]

We switched to maximal footprints in order to pick up places like the southwest corner near Santa Cruz. With the switch to bounding box filling, covering empty pixels now produces transparencies in the resulting output. Switching back to minimal footprints (and buffering the bounding box) should eliminate the voids and pick up places that would have been missed previously.

[nvkelso]

Noting here this mostly affects terrain data, not aerial imagery data.

[mojodna]

There are 3 steps to this:

• [ ] switch back from using gdalwarp to rio shapes in marblecutter-tools
• [ ] re-generate footprints for terrain data
• [ ] add buffering to the bounding box query (probably in pixels). Cf. how mapnik handles buffer sizes.

[mojodna]

Also look into rio's --with-nodata option (in addition to / conditionally instead of --mask); with bbox filling, unmasked water areas need to be seen as uncovered to pick resolution to use behind them.