Part-to-whole charts
What are they?
Part to whole charts show the distribution and relationship of individual components that make up a whole. The whole can be shown as circle (where the parts are wedges), a bar (made up of segments), a rectangle (made up of other rectangles) or areas under a curve, depending on the chart type. Examples of these charts include stacked bar charts, pie charts, donut charts, treemaps and stacked area charts.
100% Stacked bar charts show data using horizontal or vertical bars. The length of each segment of the bar represents a different category’s contribution to the total. The length of all the segments combined together represents the whole.
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Consider other chart types before using
Consider other chart types before using charts with this label. They might be appropriate, but less familiar charts are often misinterpreted—book office hours with the data viz team if you’re unsure.
Part-to-whole chart guidelines
Include all parts of the whole in pies
If you’re making a pie chart, make sure you include all of the parts and that they add up to 100%. If you don’t, the chart may have unexpected proportions. For example, a user expects to see 50% corresponding to half a pie but if parts are left out, 50% could be larger than half. If you’re showing only selected parts of the whole, use a stacked bar instead.
Avoid pie charts for comparison
It is difficult to compare segments in pie charts. If you need to compare two or more “wholes” use stacked bars or an area chart.
Not too many segments
When using a pie chart, try not to use more than 4 or 5 segments. If you need to show more than that, consider a stacked bar and also think about ways to simiplify the data. Can you combine segments? Can you highlight the most important segments somehow?
Use colors that are easily differentiable
Make sure that colors used for the wedges are easy to tell apart. This is especially important if you’re using a legend rather than direct labeling.
Use color to highlight the most important category if there is one
Color is an effective way to highlight the most important segment of a pie chart. If you’re using color to highlight a segment, make sure one that color is more prominent than the others.
Use shades of gray to de-emphasize segments that are less important
If highlighting a single segment in a pie chart, shades of gray are a good choice for less important segments.
