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First, remember your viewer is

  • Exhausted

  • Busy

  • Indifferent

 

Why graphs?

  • Visual patterns supplement our limited working memory
    • This means we can't hold all the individual data points in our head
    • But we can look at a picture to see a pattern


Limits of "typical" human perception

  • Universal design
    • Size of visualization elements (text, symbols, lines)
  • Perceptual accuracy and "ordered elementary tasks"

Top three

  1. Position along a common scale (common baseline)
  2. Position along identical, non-aligned scales (small multiples)
  3. Length, when proportionately large change

More difficult to judge

  • Angle/slope
    • We can do slopes, but not angles (this is part of why pie charts difficult)
  • Area
  • Volume
  • Color hue - color saturation - density

When in doubt

  • Pick the representation least likely to mislead
  • Use more than one representation for each variable for redundancy
    • For example, both shape and color for points

References