Pie charts are only good for one purpose and that is to reinforce part to whole relationships. They shouldn’t be used to any precise degree other than to make a point that several things make a whole. A perfect example in how to use a pie chart was during one of RIM’s bigger BlackBerry developer conference.
As you can see above when you are trying to show that two components make up 100% or at most four components make up 100%. It is very easy for us to interpret that and link the components to being a part of a whole. If you start using pie charts to show more than four components I suggest using a bar graph. This would allow you to sort them from greatest to smallest and provide the reader an easier time interpreting the data.
Pie charts is a tool that is to be used for a specific task like any other graph or visual so there are some things you must avoid at all costs!
- If it doesn’t add up to 100% then don’t use a pie chart.
- If you start using data labels, legends with data values, and the kitchen sink to show the detail you require then don’t use a pie chart.
Pie charts do have there place in the world but you must use them appropriately and don’t force it if their are other graphs which can do the job better!