26/4/2013

A Survival Guide for Data Visualisation

 

The following tips are from Gregor Aisch, visualization architect and interactive news developer, based on his workshop, Making Data Visualisations: A Survival Guide. The workshop is part of the School of Data Journalism 2013 at the International Journalism Festival.

Charts

  • Avoid 3D-charts at all costs. The perspective distorts the data, what is displayed 'in front' is perceived as more important than what is shown in the background.
  • Use pie charts with care, and only to show part of whole relationships. Two is the ideal number of slices, but never show more than five. Don't use pie charts if you want to compare values (use bar charts instead).
  • Always extend bar charts to the zero baseline. Order bars by value to make comparison easier.
  • Use line charts to show time series data. That's simply the best way to show how a variable changes over time.
  • Avoid stacked area charts, they are easily misinterpreted.
  • Prefer direct labeling wherever possible. You can save your readers a lot time by placing labels directly onto the visual elements instead of collecting them in a separate legend. Also remember that we cannot differentiate that many colors.
  • Label your axes! You might think that's kind of obvious, but still it happens quite often that designers and journalists simply forget to label the axes.
  • Tell readers why they should care about your graphic. Don't waste the title line to simply say what data is shown.

Color

Colors are difficult. They might make a boring graphic look pretty, but they really need to be handled with care.

  • Use colors sparingly. If possible, use only one or two colors in your visualization.
  • Double-check your colors for the color blind. You can use tools such as ColorOracle to simulate the effect of different types of color blindness.
  • Say goodbye to red-green color scales. A significant fraction of the male population is color blind and have problems differentiating between red and green tones. Red-blue or purple-green are common alternatives.
  • In doubt, use color scales from colorbrewer2.com

Maps

  • Don't use the Mercator projection for world maps. The distortion of area is not acceptable. Use equal-area projections instead.
  • Size symbols by area, not diameter. A common mistake is to map data values to the radius of circles. However, our visual system compares symbols by area. Use square root to compute radii from data.

Recommended reading

The slides that accompanied this workshop can be found here

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