Graphics Reference
In-Depth Information
Figure
.
.
Evolution of UNIX operating system; directed graph layout produced by Graphviz
(Pixelglow sotware), courtesy Ian Darwin, Geoff Collyer, Stephen North and Glen Low
Treemaps
5.3.5
Treemaps are recursive partitions of a space. he simplest form is a nested rectan-
gular partitioning of the plane (Johnson and Shneiderman
). To transform a bi-
nary tree into a rectangular treemap; for example, we start at the root of the tree.
We partition a rectangle vertically; each block (tile) represents one of the two chil-
dren of the root. We then partition each of the two blocks horizontally so that the
resulting nested blocks represent the children of the children. We apply this algo-
rithm recursively until all the tree nodes are covered. he recursive splits alternate
between vertical and horizontal. Other splitting algorithms are outlined in Bederson
et al.
).
If we wish, we may color the rectangles using a list of additive node weights. Oth-
erwise, we may use the popular device of resizing the rectangles according to the
node weights. Figure
.
shows an example that combines color (to represent poli-
tics, sports, technology, etc.) and size (to represent number of news sources) in a vi-
sualization of the Google news site. his map was constructed by Marcos Weskamp
and Dan Albritton.
