A circular barplot is a plot where each bar is displayed along a circle instead of a line. Here no Y scale is displayed since exact values are written on each bar which could also be represented on interaction with the chart. The chart is popular for its visual appeal however and needs to be used with caution since groups do not share the same Y-axis.
What: Discover Proportion, Rank
Why: Circular representation for aesthetic appeal
History of Circular Barplot
Circular bar plots evolved out of bar charts as a substitute to represent data when required to make the visual data story look aesthetically pleasing. As humans are naturally drawn to circles and curves these charts became more popular however circular visuals also came in conflict with the effective communication of data. It tends to serve well when one’s goal is especially to present an attention-captivating chart and get an aggregate sense of the data.
When to Use a Circular Barplot
1When the number of bars to be represented are large
Use a circular barplot when an obvious pattern pops out of a bar chart which has a large number of bars. This circular bar chart can become eye-catching in that case and make better use of the space than a long and usual barplot. However, since a circular barplot is based on a general bar chart it is essential to have a good understanding of how barplot works before making it circular.
2When your stacked bar chart looks cluttered with bars
Use a stacked circular bar chart when required to represent multiple categories, just as in a stacked bar chart except the fact that this stacked chart consists of a larger number of bars. In such a case, circular barplot can get even more interesting with a grouping variable as it becomes easy to compare groups and entities into each group. Also if the levels of your categoric variable have no obvious order, it is useful to order the bars following their values while representing in a circular plot.
3To visualize smaller number of bars in a visually appealing way
Use a radial layout barplot when there are a fewer number of bars and the chart needs to be used to add to visual appeal. This chart although is plotted using the polar coordinates however it may impede comparison, so consider them primarily to emphasize cyclical patterns. For Radial Bar Charts it is important to note that each bar on the outside gets relatively longer to the last, even if they represent the same value as each bar has to be at different radii, so each bar needs to be judged by its angle.
Types of Circular Barplot
1. Stacked Circular Barplot
These charts are arranged from highest to lowest incidence.
2. Radial Barplots
A barplot plotted on a polar coordinate system, rather than on a cartesian one.
3. Double Circular Barplot
A chart where two numeric variables are available for each group of the dataset, and are facing each other on the chart.
When Not to Use a Circular Barplot
1When knowing the exact value of the bar sizes is required
Do not use circular bar charts when exact bar sizes need to be known. The circular bars can be skewed in size if the proportion of the inner circle is not huge (>1/2). This can distort reality as the biggest of the bars can even look even bigger than they are.
2If the bar plot does not have a clear emerging pattern
Do not use circular bar plots when you do not have many levels to display (> ~40) and nor a clear emerging pattern to represent. Also when there are several values per group, circular bar plots can fail to work even with error bars, as it hides information and other types of graphics like boxplot or violin can be more appropriate.
3When required to comparing the data intricately
Use a standard bar chart or lollipop plot when required to display the information more accurately. As our visual systems are better at interpreting straight lines, so the Cartesian bar chart is a better choice for comparing values than polar and radial coordinates.