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Fig. 7.3
Shneiderman
TreeMap algorithm
Fig. 7.4
Different layouts of the same hierarchy using different algorithms. (
a
) Squarified (
Bruls
et al.
,
2000
). (
b
) Ordered (
Bederson et al.
,
2002
). (
c
) Voronoi TreeMap (
Balzer & Deussen
,
2005
)
Fig. 7.5
Use of the gap and cushion to emphasize hierarchical structure. (
a
) The basic algorithm
computes the plain underlying cell structure. (
b
) The TreeMap is augmented with a cushion effect
to enhance the nesting structure
the hierarchy (see Fig.
7.5
b). Gaps between cells can also be added. As shown
in (
Wattenberg & Fisher
,
2003
), gaps play a very important role in the human
perception of levels. Adding gaps between cells in the TreeMap can better illustrate
different hierarchical levels (see Fig.
7.6
a). In (
Lü & Fogarty
,
2008
), offsets illus-
trate the relationships between elements as an alternative to nesting (see Fig.
7.6
b).
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