I'm writing a script to combine regions rendered out from squaremap into one big image, and where I have the user specify their zoom level I wanted to write in the blocks per pixel for each one, just to give some more information. 3 seems to be 1 block per pixel, 2 looks like 4 blocks per pixel, but beyond that I can't quite tell.

It's powers of 2; 1x1, 2x2, 4x4, etc

See https://github.com/jpenilla/squaremap-stitcher for an existing tool to stitch squaremap images