Treemap visualization of hierarchical data was introduced in 1991 by Ben Schneiderman from the University of Maryland. Purple Tree uses a modified version of the Squarified layout algorithm introduced by Jarke J. van Wijk et al. This layout avoids high aspect ratio rectangles making comparison of two areas easier. The areas of two files of equal size should appear as equal for the same tree layer. However, the nested file drawing may alter the apparent area because of the margins, so thin margins lead to more visual accuracy.