Is it time for another post about the ubiquitous pie chart? Sure!
Recent questions in various online forums
- I want to use labels instead of a legend around my pie chart to make it easier to see which slice goes with which category. Sometimes these labels overlap each other in areas where the values are small. Is there any way to prevent the labels from overlapping?
- I have a pie chart where I want to show values on the chart, but the values blend together on the small slices and look a mess.
- In my pie chart, how can I prevent Excel from treating negative values as if they were positive (Excel uses the absolute value)?
- I had to re-format a graph in Excel because the person for whom it was prepared is colorblind. The very distinct (to me) red and green lines on the graph were indistinguishable to him.
- I have a bunch of pie charts, and I can’t get them to look the same size.
My responses to these questions
Rather than a pie chart, make a nice bar chart, oriented with horizontal bars. The labels run along the left edge of the chart, and they don’t overlap because they are equidistant. Numerical value labels are less important in a bar chart, because they are not needed to help compare values.
All data points (bars) in the bar chart are easy to compare because they share a common baseline, the axis along the left edge of the chart. Each data point (wedge) in the pie chart starts where the previous one ends, so there is no common baseline.
The bars encode their values using length, and all bars are aligned in the same direction, making comparison so easy. The wedges encode their values using angles or areas, which humans do not perceive as accurately as length. Since the wedges are all misoriented, it is even harder to make accurate comparisons.
The small data points (wedges in the pie, bars in the bar chart) are easier to see in the bar chart.
All of the bar colors in the bar chart are the same, so a colorblind individual can interpret its contents as easily as a person with normal color vision. If you wanted to highlight one point or a group of points, you could pick two colors that can be distinguished by people who have any color vision issues.
Pie chart with legend: identifiers are far from data points.
Pie chart with labels: identifiers are close to data points, but overlap.
Pie chart with value labels: values are hard to read on smaller data points.
Bar chart: category labels are close to data and legible,
data labels are not necessary.
Negative values in bar charts are plotted in the reverse direction, accurately indicating absolute value and sign of the data. Negative values in pie charts should be undefined, but Excel plots them as positive values.
Pie chart with negative values: you would never know unless
you looked closely at the value labels.
Pie chart with negative values and precentage labels:
percents are deceptively not presented as negatives.
Left: Bar chart with negative values: negatives clearly go opposite direction from axis.
Right: Bar chart with inverted colors for negative values: a visible clue that the values are negative.
Multiple pie charts are a bad idea made N times worse. It is very difficult to compare wedge angles on separate pies: there is no common baseline and the wedges may be misaligned. You end up with something that looks like you need a stereoscopic viewer to read.
You can put multiple sets of bars into a single bar chart, and get an instant comparison among each pair of bars. There is no need to make different charts the same size, because you have only one chart. When there are a lot of bars, you can unclutter the visualization if you use a dot plot.
Dual pie charts for comparing values: who are we fooling?
Left: Two series bar chart for comparing values: effective albeit cluttered.
Right: Two series dot plot for comparing values: effective and clean.
Previous pie chart related articles on this web site
- Bar graphs vs. Pie charts
- 3D Pie Charts
- Pie Chart Rounding in Excel
- Paper Pie Charts?
- Pie Chart for Pi Day
- Pie Chart Plotting Deficiency
- Pie Chart Traffic Light
- Column Chart to Replace Multiple Pie Charts
- How to Make a Donut-Pie Combination Chart
- Pizza Pi
- Peltier Loves Pie
- Peltier Goes Bar Hopping
- 9 Steps to Simpler Chart Formatting
- Stick a Chart in it
- Scary Info Graphic
- Ineffective Chart – Partition Chart
- Ineffective Chart – Partition Chart Revisited (Defragged)
- Seth’s Three Laws of Great Graphs
- On Seth Godin on Charts
Wow, that’s a lot!