Taxonomy of Data Visualization Methods - Data Visualization: A Successful Design Process - page 142

An example of parallel sets is given in the following image:
Image from "Parallel Sets" ( http://eagereyes.org/parallel-sets ),
created by Robert Kosara and Caroline Ziemkiewicz
Radial network (or chord diagram)
Data variables : Multiple x categorical, 2 x quantitative-ratio.
Visual variables : Position, connection, width, color-hue, color-lightness, symbol, size.
Description : A radial network or chord diagram creates a framework for comparing
complex relationships between categorical values. The use of a radial layout offers
the opportunity to move beyond the restrictions of an x and y axis pairing. The key
explanatory property is the connections that exist between components, sometimes
sized (thickness) and colored to incorporate extra layers of detail. In the following
example, we see additional levels of detail represented by the encoded size of text
and icons. One thing to note is that the length (and therefore prominence) of a line
can slightly mislead by inferring significance (a more important relationship) when
it is simply a by-product of the arrangement around the radial layout.