¶ 1 Leave a comment on paragraph 1 0 Luckily for us, there are a few gauges for choosing between visualization types and graphic variables that go beyond the merely aesthetic. Social research has shown various ways in which people process what they see, and that research should guide our decisions in creating effective information visualizations.
¶ 2 Leave a comment on paragraph 2 0 About a tenth of all men and a hundredth of all women have some form of color blindness. There are many varieties of color blindness; some people see completely in monochrome, others have difficulty distinguishing between red and green, or between blue and green, or other combinations besides. To compensate, visualizations may encode the same data in multiple variables. Traffic lights present a perfect example of this; most of us are familiar with the red, yellow, and green color schemes, but for those people who cannot distinguish among these colors, top-to-bottom orientation sends the same signal. If you need to pick colors that are safely distinguishable by most audiences, a few online services can assist. One popular service is colorbrewer (http://colorbrewer2.org/), which allows you to create a color scheme that fits whatever set of parameters you may need.
¶ 3 Leave a comment on paragraph 3 0 In 2010, Randall Munroe conducted a massive online survey asking people to name the colors they were randomly presented. The results showed that women disproportionately named colors more specifically than men, such that where a woman might have labeled a color as neon green, a man might have just named it green. This does not imply women can more easily differentiate between colors, as some occasionally suggest, although part of the survey results definitely do show the disproportionate amount of men who have some form of color blindness. Beyond sex and gender, culture also plays a role in the interpretation of colors in a visualization. In some cultures, death is signified by the color black; in others, it is signified by white. In most cultures, both heat and passion are signified by the color red; illness is often, but not always, signified by yellow. Your audience should influence your choice of color palette, as readers will always come to a visualization with preconceived notions of what your graphic variables imply.
¶ 4 Leave a comment on paragraph 4 0 Gestalt psychology is a century-old practice of understanding how people perceive patterns. It attempts to show how we perceive separate visual elements as whole units–how we organize what we see into discernible objects (figure 5.29). Among the principles of Gestalt psychology are:
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- Proximity. We perceive objects that are close together as being part of a single group.
- Similarity. Objects that are visually similar (e.g. the same color) will be perceived as part of a single group.
- Closure. We tend to fill in the blanks when there is missing information; if we see a box of which two corners are absent, we will still see the box as a single unit, rather than two disjointed line segments.
¶ 8 Leave a comment on paragraph 8 0 These and other gestalt principles can be used to make informed decisions regarding graphic variables. Knowing what patterns tend to lead to perceptions of continuity or discontinuity is essential in making effective information visualizations.
¶ 9 Leave a comment on paragraph 9 0 At a more fine-grained level, when choosing between equally appropriate graphic variables, research on preattentive processing can steer us in the right direction. We preattentively process certain graphic variables, meaning we can spot differences in those variables in fewer than 10 milliseconds. Color is a preattentively processed graphic variable, and thus in figure 5.30, you will very quickly spot the dot that does not belong. That the processing is preattentive implies you do not need to actively search for the difference to find it.
¶ 12 Leave a comment on paragraph 12 0 Size, orientation, color, density, and many other variables are preattentively processed. The issue comes when you have to combine multiple graphic variables and, in most visualizations, that is precisely the task at hand. When combining graphic variables (e.g. shape and color), what was initially preattentively processed often loses its ease of discovery. Research into preattentive processing can then be used to show which combinations are still useful for quick information gathering. One such combination is spatial distance and color. In figure 5.31, you can quickly determine both the two spatially distinct groups, and the spatially distinct colours.
¶ 16 Leave a comment on paragraph 16 0 Another important limitation of human perception to keep in mind is change blindness. When people are presented two pictures of the same scene, one after the other, and the second picture is missing some object that was in the first, it is surprisingly difficult to discern what has changed between the two images. The same holds true for animated / dynamic visualizations. We have difficulty holding in our minds the information from previous frames, and so while an animation seems a noble way of visualizing temporal change, it is rarely an effective one. Replacing an animation with small multiples, or some other static visualization, will improve the reader’s ability to notice specific changes over time.