There's a bit of an issue with the linked deployment (in my opinion). In the most zoomed out view you should see the first layer of blocks - very big blocks titled "English language", "French language", "German language". See https://phiresky.github.io/isbn-visualization/ maybe. That makes it a bit easier to read.

The point of the visualization is showing different attributes of books in the space of ISBNs. ISBNs correlate with country, publisher, and release date, that's why using it as a space is useful. You can clearly see the history of when blocks were created, which blocks are rarer than others (present in fewer libraries), and (on the AA hosting) which blocks are more present in AA vs not.

In any case though, yes ISBNs as spatial data are clearly not perfect. Do you have any suggestions that would order the 100 million data points better?