ContentsPie charts

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Although pie charts are very useful and simple, I've deferred them until now to be sure you had a good understanding of what is going on. If you've skipped to this section from the table of contents, please (at least) look over the section on basic charting before continuing.

The reason pie charts are so useful is that they have so many limitations. You absolutely must be comparing the same kind of data... not data which is merely related through a common attribute, such as time. Given that restriction, you really only have one value set to work with. Different colors are used to represent different values (instead of a whole set of values, as is the case for regular charts).

In the last example, we created a bar chart with a repeating pattern effect to show comparisons between different values of the same kind of data. Conceptually, a pie chart is just a different rendering of this information which uses a complete circle and allows different values to be compared with each other by their angular portion (i.e. the percentage of the total of the values). In that example, you may have wanted to improve on the legend by showing different bars with different colors. You might have been tempted to do this by adding another set of values, but this would have been confusing to the person reading your chart. That's where the need for pie chart representations come from.

If that explanation is too convoluted, let me state it more simply: pie charts visualize how each value compares to the whole on a percentage basis.

ContentsPie charts

Previous: Coding a new ValueSet type | Next: Why pie charts are different