Chartjunk
As with bar charts, pie charts are often graphical representations of a small number of values. For example, a pie chart of the gender of students in a class is only based on a single value, the proportion of males. As a result, there is a temptation to 'enhance' pie charts as 3-dimensional objects — chartjunk.
Resist the temptation — it does not make the data any easier to understand and may indeed be misleading since 3-dimensional pie charts can over-emphasise the categories closest to the viewer.
Tourist expenditure in Hawaii
The pie chart below describes the money that tourists spent in Hawaii in 2006. (The total tourist expenditure was $12,380,900,000 in that year.)
This diagram is 3-dimensional. Press the mouse in the centre of the pie chart and drag (with the mouse held down) towards the top left to rotate the diagram. The slider can be used to alter the thickness of the pie.
The simple pie chart is equally effective for displaying the data. If the rotation is extreme or the pie is thick, the rotated pie chart can exaggerate the importance of the front categories.
Variations
The following diagrams show other 3-dimensional variations of the basic pie chart. In both cases, the extra dimension is chartjunk — neither improves on a basic 2-dimensional pie chart.
Local authority income
The doughnut chart below describes the sources of income of New Zealand local authorities in 1996.