SpinachThief

I was inspired to import map data from an ancient console favorite. I was hoping to find a grid of single byte values in the ROM image. Searching the file for in-game rock patterns in rows didn't turn up any hits. Searching for column patterns did sometimes but the columns themselves were never in any comprehensible order. This hacking guide explains most of how game screens are built with pre-assembled (and further compressed) 11 square columns to save space. There are a number of other compression methods like storing palettes seperately for the center of the screen and for the outer two rows. These methods must have complicated design and also dictated the final product to some extent but even so the resulting "overworld" map is skillfully crafted.

P.S. I should add that I wasn't able to reconstruct 100% of the column tables and ended up just repairing them manually. The hacking guide doesn't mention that if a new column is started before the previous column is described in full that the first tile or double tile of the next column in that column table will also be rendered where the previous column left off. If the previous column still hasn't been fully described then I'm not sure where the remaining tiles are coming from. Not from anywhere in that column anyway. Also instead of 4 duplicate screens there are 7: A7->A9, A12->D13, D10->E3, E3->E4, F16->E16, A7->H11, H13->H14.