During the 1990s Ben Shneiderman of the Human-Computer Interaction Laboritory (HCIL) at the University of Maryland invented Treemaps as a compact visualization of directory tree structures. Treemaps involve turning a tree into a planar space-filling representation using assorted boxes-in-boxes algorithms.

I've lately coded on a new, fresh, evolutionary dead-end approach to disk-usage visualization using nested circles instead of boxes: circular treemaps or pebble treemaps.

On the weekend I set up a page with explanations and screenshots about pebble treemaps.