http://www.functionalelegance.com

History

• John Snow's cholera investigation; plot dots on a map

"Hockey stick" chart

• Famous climate change temperature change chart; controversial
  • All down to the axis scale!
  • Such a simple choice is a frame; we choose to present a bias, honestly or not.

Aspect ratio

• Another simple question! How do you choose it?
• 1:1 - fair?
• 3:2 - landscape?
• golden ratio - beautiful?
• average slope 45 degrees - perceptually optimal for orientation discrimination.
  • easiest angle to see deviations in trend (rather than horizontal / vertical)
• but graphic designers know - all choices depend on what story you want to tell
  • choices inevitably affect this.

 Map projections

• Mercator - preserve angles, not areas.
  • used for shipping / navigation
• Choices are frames. You understand "3D projections onto 2D are necessarily imperfect", but ordinary people just blindly accept the frame.
• Robinson - almost preserve area, not angle
• But why not plot, scaling for GDP and population, not area? Surely more informative.

Choices

• Representing numeric values without misleading users - our goal.
• Difficult to judge area of quadrangles
  • Yet we use quadrangular heat maps!
• Ebbinghaus Illusion: very difficult to perceive areas of circles based on context
  • But we use bubble charts!
• Even if you use numeric labels, it's too late. Your users have made judgements visually.
• Can't distinguish colours if they're next to other colours
  • Yet we use heat maps!

Context

• Add context!
  • Textual callouts
  • Don't use many colour graduations, few
  • Different charts on same page for different views - allows different perspectives, robust.
• The more people are paid, the less able they are to read charts.
• Use familiar idioms
  • Next to a vertical bar chart, add traffic lights! Green is up, red is down, yellow is OK.
• "Familiar visual metaphors make interpretation easier"

Colour gradients

• Don't use rainbow palettes for continuous numeric values.
• We always see edges between hues (turns categorical).
• Yellow stands out too much
  • Use iso-luminate palette, yellow turns brown.
• Brain can distinguish brightness much better than hue.

Transparency layering

• !!AI see presenter's website for info; different ways of mixing layers.

Sphere of Influence graphs

http://demonstrations.wolfram.com/SphereOfInfluenceGraphs/

Graphs

http://visualization.geblogs.com/visualization/network/

Summary

• Since framing is inevitable, start with the user and their context and objecives.

Questions

• Given interaction or offer multiple simultaneous views, which to do?
  • Interaction always wins.
  • Multiple charts will often leave users confused.