![]() ![]() In the space taken by a pie chart with five data points we can easily display a scatter plot with hundreds of data points. This means that the real estate needed to display a single data point is excessive. A third argument is that is a very low density chart.The more slices the less variation between them, so the harder to compare the arcs/angles/areas. With more than, say, five or six slices the chart becomes overcrowded and even more difficult to read. A second argument is that you can’t use many data points.The pie above confirms this: it’s very hard to say which one is the largest slice. Research tells us that people do a very poor job at measuring angles and semi-arcs and comparing areas.Pie charts are the data visualization expert’s pet peeve. Perhaps more interesting, the first two slices account for more than half of the whole. What can we read here? The first slice accounts for around one third of the whole. How do you read a pie chart? Research shows that people compare slices based on one of three measures: length of semi-arcs, angles and slice area: Now you understand the origins of a pie chart:Īs you can see, we first map the distances between data points, then stack them, connect them with a thick line (looks like a stacked bar chart), bend them and finally remove the hole to get the pie chart. If you haven’t read the page What is a chart I recommend you do it now. Categories must be seen as parts of a meaningful whole. ![]() Collectively exhaustive categories (all data points in the whole must be represented).Mutually exclusive, non-overlapping categories (a data point cannot belong to more than one slice).To make a pie chart your data should consist of: You are likely to see a lot of pies in a market research report also. In the corporate world, market share is the obvious example of data that can be represented with pie charts. The pie is a circular chart used to display proportions of a whole. Let them decide if they still love pie charts.Show them how abusing pie charts can be bad for business. ![]()
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