THE MULTIPLE VISUAL ATTRIBUTES OF SHAPE - Information Visualisation: Techniques, Usability and Evaluation - page 56

Fig. 3.20. Email visualization relying on glyph concavity to indicate read state.
For any shape attribute, multiple factors may be available to define that
attribute. A terminator at the end of a line or on a corner may have many
possible options, including length, height, fill, closure, etc. There is the
potential to apply recursive principles to shape attributes, with limits
determined by the size of the object and the quality of the resolution - e.g.
there are not many options for terminators if the space available is only 2 x
2 pixels; but with interactive zooming techniques, lower priority data
variables could be encoded in a serif that becomes visible when zoomed
in.
Fig. 3.21. Possible sub-attributes for terminators, including type, closure, fill.
As the experimentation progressed simultaneously with the background
research, new attributes and new experiments were considered to evaluate
other potential shape attributes. Some examples of the different attributes
tested include: concavity/notch/spike, curvature, serifs, angle, edge-
type/line-style, and local warp (Fig. 3.22).