Update: A few commentators were looking for alternatives to the pie chart. The alternative recommended by almost everybody in this list is the simple bar chart. Here is a perspective from Stephen Few:
But what if we could display this same information in a graph that is easy to read; one that adds useful meaning by allowing us to compare the magnitudes of the values without labeling them? Now the values can be compared with relative ease and precision, relying solely on the graph, without labeling the values. What value does this bar graph offer, compared to a table? In little more than a glance it paints a picture of the relationships between six companies regarding market share. Not only is their relative rank apparent, but the differences in value from one company to the next is readily available to our eyes. Could we construct this same picture in our heads from a table of the same values? Perhaps, but it would take a great deal of effort and time. Why bother when a graph can do the work for you and tell the story in a way that speaks directly to the high-bandwidth, parallel imaging processor in your brain, which operates much faster than the part of your brain that handles text, which is needed to process tables?
Pie Chart Vs Bar Chart Example
In our analytics careers, we would have made at least one pie chart to show the output of our data & then had a slightly nagging uncomfortable feeling about it. Here are 10 resources by experts & practitioners to help you stop making pie charts & make that uncomfortable feeling go away.
1/ Edward Tufte, the god of visualization in his landmark book “The Visual Display of Quantitative Information”
A table is nearly always better than a dumb pie chart; the only worse design than a pie chart is several of them, for then the viewer is asked to compare quantities located in spatial disarray both within and between charts [...] Given their low density and failure to order numbers along a visual dimension, pie charts should never be used.
Pie charts are not without their strengths. The primary strength of a pie chart is the fact that the message “part-to-whole relationship” is built right into it in an obvious way. Children learn fractions by looking at pies sliced in various ways and decoding the ratio (quarter, half, three quarters, etc.) of each slice. A bar graph doesn’t have this obvious purpose built into its design. Not as directly, anyway, but it can be built into bar graphs in a way that prompts people to think in terms of a whole and its parts. This can be accomplished in part by using a percentage scale. It is easy and natural to think in terms of various percentages in relation to the whole of 100%. Seeing a bar extend to 25% along a quantitative scale conveys a part-to whole relationship only slightly less effectively than a pie chart with a quarter slice, especially if the bar graph’s title declares that it displays the parts of some total (for example, “Regional Breakdown of Total Revenue”). Despite the obvious nature of a pie charts message, bar graphs provide a much better means to compare the magnitudes of each part. Pie charts only make it easy to judge the magnitude of a slice when it is close to 0%, 25%, 50%, 75%, or 100%. Any percentages other than these are difficult to discern in a pie chart, but can be accurately discerned in a bar graph, thanks to the quantitative scale.
3/ Story Telling with Data: My main beef with pie charts is this: our eyes aren't good at attributing quantitative value to two dimensional spaces. In English: pie charts are really hard for people to read! When segments are close in size, it'd difficult (if not impossible) to tell which is bigger. When they aren't close in size, the best you can do is determine that one is bigger than the other, but you can't judge by how much.
Problem 1: pie charts are bad at communicating the basics
Problem 2: pie charts are worse at showing trends
Problem 3: pie charts are terrible at showing trends in absolute numbers
Number 10 - Pie Charts Just Don't Work When Comparing Data
Number 9 - You Have A Better Option: The Sorted Horizontal Bar Chart
Number 8 - The Pie Chart is Always Round
Number 7 - Some Genius Will Make It 3D
Number 6 - Legends and Labels are Hard to Align and Read
Number 5 - Nobody Has Ever Made a Critical Decision Using a Pie Chart
Number 4 - It Doesn't Scale Well to More Than 2 Items
Number 3 - A Pie Chart Causes Distortions and Errors
Number 2 - Everyone Else Uses Them: Debunking the "Urban Legend" of Pie Charts
Number 1 - Pie Charts Make You Look Stupid and Lazy
6/ Bernard Marr, a consultant on analytics & data: From a design point of view, a pie chart takes up far too much space to convey a set of data compared to other options. In addition, the labels don’t line up, so the result becomes cluttered and hard to read — strike three against pie charts, as they often make the data more complicated than before. Pie charts also don’t work well at various sizes. A small pie chart is all but useless, whereas a small bar graph or line graph can still easily show differences in data.
7/ Evolytics - An analytics firm : Your brain processes heights of bars more easily than it process areas in a pie. Using a bar chart also provides you more real estate to display the values, either as dollar amounts and/or percents of the whole (as you were trying to convey by using a pie chart). To take this one final step further, if you only care about comparing how each category performed against the others for one period in time, you can isolate the bar chart to show just the year in question.
8/ Business Insider: The reality is, humans aren't very good at comparing slices of a circle when it comes to size. It's the reason you probably found trigonometry and radians a lot more difficult than you found basic rectangle geometry.
ARGUMENT ONE – COMPARING INDIVIDUAL VALUES
ARGUMENT TWO – SIZE MATTERS
ARGUMENT THREE – COMPARING COMBINED VALUES
Pie charts rely on colors to differentiate the data and the color differences are not easily apparent
Pie charts labels are much hard to link to the data
Pie charts suck at the small percentages.
Pie chart are not easy to spot small differences
Pie charts use a lot more space than bar charts & have more white space