INFORMATION VISUALIZATION ON SPHERES - Information Visualisation: Techniques, Usability and Evaluation - page 33

revealed in more detail in the next step, similar to the literary device of
foreshadowing.

Fig. 2.11. Treemap on sphere (left) obscures internal structure and backside.
Treemap with gaps (centre) shows inner treemaps (also with gaps) but perceptually
difficult to parse the tree segments at various levels of hierarchy. Treemap on outer
shell with ball and stick hierarchy inside sphere (right).

Data for SphereTree included:

• Consumer Price Index : a hierarchy of common goods purchased

by U.S. consumers, including the proportion of household spending
and changes in price over the previous period.

• Occupations and Incomes : a hierarchy of occupations, with

attributes such as number of people employed in the profession,
average income, and change in income.

• Stocks : a hierarchy of 500 stocks with attributes of volume and

price.

SphereCorr and SphereTree visualizations are viewable at http://www.
oculusinfo.com/assets/demos/SphereTreeDemo/

Incremental refinement of sphere visualizations

During development and initial user testing, unexpected design
refinements were required:

x Depth perception : Distinguishing the depth of different elements -

front half of the sphere, back half of the sphere and intermediate
shells - was difficult to do in a static scene. A very slow rotation
was added to improve 3D depth perception [Wic89]. This helped
discriminate foreground and background in simple scenes (e.g.
SphereCorr) but was insufficient to disambiguate fully the multi-
shelled SphereTrees. Additional white outlines around foreground