One thing it shows is how ISBNs are allocated much faster than they are used, judging by the amount of black pixels.
The image contains 1000*800 pixels at 2500 ISBNs per pixel, so it's visualizing 2e9 ISBNs. ISBN-13 contains 12 digits plus one check digit, so we might have expected the image to be 500 times bigger/denser than the current image. The fact that it's at its current size suggests that only ISBNs with 978 and 979 prefixes are included, and since the bottom half is more sparse, that probably corresponds to the new 979 range.
The image contains 1000*800 pixels at 2500 ISBNs per pixel, so it's visualizing 2e9 ISBNs. ISBN-13 contains 12 digits plus one check digit, so we might have expected the image to be 500 times bigger/denser than the current image. The fact that it's at its current size suggests that only ISBNs with 978 and 979 prefixes are included, and since the bottom half is more sparse, that probably corresponds to the new 979 range.