I finally took Edward Tufte’s day-long information design course last week. Tufte, long a thought leader on the topic of graphically showing quantitative and scientific data, shared his principles for displaying this evidence in any media. Here are my notes:
- Designers of data displays, either printed or online, should strive to reduce the time it takes to learn the display format and increase the time the reader devotes to thinking about the data.
- Use “small multiples“, repeated use of the same type of graphic, to reduce learning time. Once a person figures out how one graphic is read, they know how to read all the graphics.
- Charts and other graphical displays should always tell stories. This often involves displaying information using a time scale.
- Data displays should supply context as well as information. A price increase from one year to the next tells little unless it is shown in the context of the past five or 10 years.
- Multi-variate data graphics supply the richest context and tell the best stories. Price increases (or declines) shown over time and compared to wage increases (or declines) for the same period tell a much more powerful story than simply showing the price increase alone.
- Keep “chartjunk” and “chartoons” to a minimum. Embellishments like gradients or patterns for the backgrounds of charts and graphs only get in the way of the information. Designers should strive for a high ink to data ratio.
- If content in a display needs to be compared to other content, put the two chunks of content next to each other. It’s unreasonable to ask a person to go back and forth between web pages or printed pages when trying to compare two or more things.
- Using area to display quantitative data is a risky proposition. Unless the scale of the area of all diagram elements exactly matches the scale of the data, the graphic is lying.
- In a related thought, the only thing worse than using a pie chart to display quantitative data is using multiple pie charts. It is impossible for people to figure out what percent of the whole is represented by the pie pieces without the numbers being displayed on the slices. And if you need to display the numbers, why not use a simple table instead.
- When designing line and bar charts, don’t place a legend off to the side. This forces people to have to scan back and forth between the graphical element and the legend. It is better to put the notation near the elements in the graph itself.
- A graphical user interface should be “invisible” so that people can focus on the information. If we as designers do our jobs correctly, people won’t be aware of our work.
I’m sure there are points I missed. All of Tufte’s principles are covered in four of his beautifully produced books that came with admission to the course. They are themselves examples of Tufte’s principles.