Squarified Treemap was introduced in the paper Bruls, Mark, Kees Huizing, and Jarke J. Van Wijk. Squarified treemaps. Springer Vienna, 2000. Link to Google Scholar
Squarified Treemap is one way to visualize hierarchical data.
The hierarchy of the input data:
0 |-1 | |-11 | |-2 | |-21 | |-22 | |-3 | |-31 | |-32 | |-33 | |-4 | |-41 | |-42 | |-43 | |-44 | |-5 | |-51 | |-52 | |-53 | |-54 | |-55 | |-6 |-61 | |-611 | |-612 | |-613 | |-62 |-63 |-64 |-65 |-66
The Processing source code is available at https://github.com/zshiba/visualization.