Like any other game console, Atari 2600 cartridges contained executable code also commingled with data. This lists the code as columns of assembly language. Most of it is math or conditional statements (if x is true, go to y), so each time there's "go to" a curve is drawn from that point to its destination.
When a byte of data (as opposed to code) is found in the cartridge, it is shown as an orange row: a solid block for a "1" or a dot for a "0". The row is eight elements long, representing a whole byte. This usually means that the images can be seen in their entirety when a series of bytes are shown as rows. The images were often stored upside-down as a programming method.
The original version of these images are a series of 13 x 19 inch prints where you can actually read the individual bits of text. I modified a version of distella to produce disassembled text output in the format that I wanted, and then used Processing to write a second program that creates the image of the output.
In response to requests, you can now purchase prints of these images.
Prints from the dismap
project are also available. All proceeds are donated to charity.
(Sorry, prints are no longer for sale! I haven't had time to support sales.)