Visualization is about perceiving features and structure in images. It is also about giving the user control over the data to analyze. As a consequence, visualization naturally links with perception issues – as well as with cognition.
Visualization interfaces fall within a category Ben Shneiderman called “Direct Manipulation Interfaces”, to refer to systems having the following properties:
Citing Hutchins et al., we can only agree with the fact that […] the feeling of directness is inversely proportional to the amount of cognitive effort it takes to manipulate and evaluate a system […]. Designing and building a visualization aims at helping users understand and interpret data, from which they can access information and potentially find new knowledge. Obstacles are on the way, as in any communication channel.
Obstacles roughly reside at three different levels, each inducing distance between the author's intention (the visualization designer) and the reader's interpretation:
(Italicized definitions are borrowed and adapted from Barbara Sheehan et al. (2009). AMIA Annual Symposium, pp. 584–588.)
Conversely, we can look at the distance the other way round and try to see whether a user can efficiently use a system. Hutcins et al. usefully consider different definitions for what they call the semantic and articulatory distances:
a conceptually simple piece of work?
Papers worth looking at:
The use of computer-supported, interactive, visual representations of abstract data to amplify cognition. [Card, S. K., J. D. Mackinlay, B. Shneiderman (1999). Readings in Information Visualization. San Francisco, Morgan Kaufmann Publishers.]
Information visualization utilizes computer graphics and interaction to assist humans in solving problems. [Purchase, H., N. Andrienko, et al. (2008). Theoretical Foundations of Information Visualization Information Visualization, Lecture Notes in Computer Science 4950, Springer Berlin, pp. 46-64.]
Think of the eye as a computing machinery. According to Ware, 40% of our cortical activity is devoted to processing visual signals. But this doesn't go without making errors. Care must be taken when designing an image to avoid the eye to misinterpret the information we want the image to carry.
Visual illusions are convincing of our visual system's flaws in interpreting visual signals.
Some signals do not rely on higher cognitive processes, but are processed immediately. Some other signals rely on higher, and lengthier, processes.
Patrick Healey's website on perception is a useful resource for understanding and experimenting with these ideas.
Color must be used with care. Cartographers have been using color schemes for decades to map quantities and/or categories. Simple color schemes include the rainbow spectrum, red-blue or red-green ramps, and the grey-red saturation scale. The use of colors must carefully seek for (borrowed from Healey):
Cynthia Brewer's ColorBrewer is a useful and authoritative source to help designers choose among all possible and most readable color schemes.
A few design principles help choose the right way to go with colors.
Exercises / Assignments