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
- Position along a common scale (common baseline)
- Position along identical, non-aligned scales (small multiples)
- 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