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Chart Design

CAPP 30239

Today

  • What general principles of visual design are relevant to our work?
  • What are the common types of charts and how do we use them?
  • When and how do we break the rules?

Edward Tufte

The Visual Display of Quantitative Information

Key Ideas

  • Graphical Integrity: Above all else, show the data.
  • Maximize the data-ink ratio.
  • Minimize chart-junk.
  • Aim for high chart density, consider small multiples.
  • Revision & Editing are essential.

Tufte's Principles for Graphical Integrity

  1. The representation of numbers, as physically measured on the surface of the graphic itself, should be directly proportional to the numerical quantities represented.

Mileage increase: 53% Graph length increase: 783% "Lie Factor": 14.8x

  1. Clear, detailed and thorough labeling should be used to defeat graphical distortion and ambiguity.

bg left

How many children get a spinal injury every year? (out of 74,000,000 children in US)

  1. Write out explanation of the data on the graphic itself. Label important events in the data.

  1. Show data variation, not design variation.

Deflated & standardized units of money are almost almost superior to nominal units.

The number of information-carrying (variable) dimensions depicted should not exceed the number of dimensions in the data. (roughly 1:1 channel mapping)

Exception: It is OK/common to pair color & shape, or for print color & texture to address issues that color presents.

Data-Ink Ratio

  • Data-ink: Ink (pixels) used to show data.
  • Data-ink ratio: data-ink / total-ink

bg right width:600px

Optimizing Data Density

Number of entries in DataFrame / Area of Graphic.

Classic example of high data density is the sparkline, which can fit on a line of text.

bg left height:700px

Chart Junk

Anything that isn't relevant to understanding the data.

via junkcharts.typepad.com

Common Chart Types

Bar Charts & Histograms

Line & Area Charts

Sparklines

Strip Plot & Heatmap

Pie / Donut / Radial Charts

Ranked Line Chart

Scatterplots

Small Multiples / Faceting

Distributions

Map Basics

Altair Gallery Miscellania

When & How to Break the Rules

2 Examples: Hex / Grid maps ... Word Clouds

Narrative-supporting graphics

When it's OK to use 3D

Acknowledgements & References

Thanks to Alex Hale, Andrew McNutt, and Jessica Hullman for sharing their materials.