I’ve said it before. We are much better at digesting visual information—position, size, color, hue—than we are at digesting words and numbers. Words and numbers, which only appeared within the last few thousand years, require our visual system to scan individual characters one at a time and piece them together to create meaning. By contrast, we can process visual cues simultaneously and very quickly. We don’t read pictures from left to right and from top to bottom. We process the elements of a picture in parallel. Very efficient.
Once you decide to represent your data visually, you need to decide how. What visual cues are right for the job? Luckily, there’s some research to point you in the right direction. Cleveland and McGill (and others) have studied what types of encodings or “channels” people are able to decode most accurately and ranked them, as shown above.
As you can see, we are great at assessing position along a common scale and pretty good at length, even without a common scale. This is one reason why bar charts are so powerful. We are less good at assessing something like color intensity. While we can see that one color is darker than the other, it’s hard to determine if it’s twice as dark.
So if you need your viewers to make more accurate assessments, use visual encodings toward the right end of the spectrum, but other encodings, toward the left end, are fine for more general assessments.
See other data tips in this series for more information on how to effectively visualize and make good use of your organization's data.