Pie charts
It has repeatedly come to my attention that people don't understand how and when to use pie charts. In general, pie charts are an inferior visualization; you almost always want a bar chart or a table or a list instead. There are very specific situations when pie charts are a reasonable choice, and there are some rules you should always follow when using them.
If your data do not comprise components of a whole, DO NOT use a pie chart. Period.
If you only have 3 or so values to compare, JUST LIST THE DATA. Or, if you need the dramatic visual effect, use a bar chart.
If you need your audience to be able to compare items in your chart accurately, DO NOT use a pie chart. Use a bar chart instead. We are built to gauge differences in line lengths, not curve lengths with misleading areas.
If your data do not comprise components of a whole, DO NOT use a pie chart. Period.
If you only have 3 or so values to compare, JUST LIST THE DATA. Or, if you need the dramatic visual effect, use a bar chart.
If you need your audience to be able to compare items in your chart accurately, DO NOT use a pie chart. Use a bar chart instead. We are built to gauge differences in line lengths, not curve lengths with misleading areas.
- If you have a bunch of values representing parts of a whole, and you don't need the audience to be able to compare them accurately by inspection:
- Always sort your data by value. I usually place the biggest slice in the rotation at 90 degrees and descend clockwise, but as long as it's sorted your audience will have a better understanding of the comparison.
- Provide clear labels, and if there's room try to fit the data on the chart or legend.
- Do not use 3D or perspective. Shame on you.