Taxonomy of Data Visualization Methods - Data Visualization: A Successful Design Process - page 148

Description : This is a technique for overcoming the flaws associated with the
choropleth map and involves combining color-hue (to represent a political party),
with color saturation (to represent the dominance of party persuasion), with a final
dimension of color-darkness to represent the density of population. Algorithms are
applied to help smooth the representation through the contour effect and this creates
an elegant end result; as shown here:
Image from "Isarithmic Maps of Public Opinion Data" ( http://dsparks.wordpress.com/2011/10/24/
isarithmic-maps-of-public-opinion-data/ ), created by David B Sparks
Particle flow map
Data variables : Multiple x quantitative.
Visual variables : Position, direction, thickness, speed.
Description : A particle flow map uses animation to portray the motion of data
across geography and over time. In the following example, we see the motion of
the currents that drive the world's oceans. These careful and highly sophisticated
constructions combine multiple variables of location, size, speed, and direction to
create a compelling design that perfectly captures the nature of the subject matter.