Graphics Reference
In-Depth Information
Figure
.
.
Regular (let) and Mondrian (right) mosaicplots of the Titanic data. Class is plotted versus
Age. he empty crew/child cell disappears from the Mondrian display
standard mosaicplot, they are not well equipped to deal with empty combinations.
Figure
.
shows two mosaicplots of the same aspect of the Titanic data: Class is
plotted against Age. he empty bin (there were, bydefinition, nochildren among the
crewmembers)disappears intheMondrian displayontheright.Sometimes,though,
particularly in data with many categories, Mondrian displays can be beneficial since
they utilize the tiny extra bit of screen space available (the spaces between the rect-
angles).
Related Work and Generalization
13.4
In contrast to the mosaicplot variants discussed earlier, this section is about actual
extensions. While the variants show the same or a reduced amount (in the case of
same-bin-size displays) of information, treemaps and trellis displays have a richer
structure than a mosaicplot; indeed the mosaicplot is a special case of each of these.
Treemaps
13.4.1
Treemaps were introduced by (Johnson and Shneiderman,
) as a method of vi-
sualizing the file structure on a hard disk used by
users, in order to determine
where and how space was used. Finding large files that could be deleted and deter-
mining which users consumed the most disk space were di
cult tasks. Treemaps
are designed to display trees, such as directory trees. Associated with each node in
a directory tree is a numeric value that gives the disk space used by the files in the
subtree rooted at the node.Each nodeis displayed as a rectangle; the size of this rect-
angle is proportional to the disk space it represents. All descendents of the node are
displayed as rectangles inside this rectangle. By default, horizontal and vertical splits
are alternated, just as in standard mosaicplots. Each file appears as a rectangle whose
size is proportional to the file size, enabling users to spot large files at any level in the
hierarchy.
