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You’ve probably seen them used in business presentations or on your favorite TV show, but did you know that pie charts are based on a mathematical concept known as polar coordinates? If you need to create one of these charts for an upcoming project, take this study guide to help you get started with the basics of how to draw pie charts using polar coordinates. You’ll also find some great examples of real-world pie charts so you can start using this technique in your work right away!
Pie charts are used in data visualization and can be useful when you want to represent parts of a whole (the whole being your data). If your pie chart’s size represents proportion, it’s called an area chart; if it represents percentages, it’s called a proportional stacked chart. Here are some examples of pie charts in action.
Introduction to Pie Chart
A pie chart is a circular data visualization used to represent numerical data. Pie charts are typically used in business to provide a clear visual representation of company sales, but they can be used for any type of breakdown of an entity. Unlike bar graphs and line graphs, pie charts tend to have low information density because they use only one shape (circle) to represent all values. However, compared with other popular circular charts like sunburst plots and radial plots, pie charts are much easier to read at first glance because their size varies based on their value. Also known as circle graphs or slice graphs, these simple graphics become powerful analytical tools when you understand how to read them correctly and utilize them effectively.
Sample Pie Chart
A pie chart has two key elements: It must show clearly which numbers belong to which parts. This can be done by marking segments of pie with letters, numbers, or colors (or using a circle), and making sure that they are different enough from each other so that you can instantly tell them apart. Not having labels within pie charts is common—they tend to take up a lot of space and they don’t add much value, but there are some exceptions. The second important aspect is making sure that all pies are equal in size and shape.
Simple vs. Fractional Parts of a Whole
Simple parts of a whole are often represented in pie charts as separate slices. Pie charts work best when you want to show one single metric and compare it to a full group or category. Fractional parts of a whole are often used to show multiple pieces of information at once. This works especially well if you have related pieces of data that need to be shown side-by-side, such as with quarterly or annual sales goals over time. In these cases, each section can represent an individual slice.
Qualitative Data Pie Charts
Before we start talking about qualitative data, it’s important to note that most of your information won’t be qualitative. But in cases where you have a small amount of data or you’re comparing two similar variables, pie charts can work as a good way to show relative comparison. For example, if your site visitors are split evenly between web and mobile visitors (each group makes up 50% of all site traffic), pie charts are a great way to compare each user type without cluttering up other figures. Qualitative data is all about expressing judgments, so a subjective point of view would make sense here! Qualitative Data Pie Charts may look something like 55% and 45% Notice how each section only takes up half of the pie? That’s on purpose!
Basic Percentage Graphs (Donut, Pie, Stacked Bar)
Percentage graphs are useful because they allow readers to see quickly and easily what percent of a whole is represented by each data value. Percentage graphs can be either circular (pie, donut) or rectangular (bar, stacked bar). Pie charts show data as sectors of a circle. Stacked bar graphs show data as rectangles arranged vertically with percentage values on top. A stacked column graph shows data as horizontal rectangles but instead of being ordered vertically by percentage, values are ordered alphabetically. In addition to showing how much of a whole is made up of each part, stacked charts also show how many units fall into different categories.
Identifying Patterns in Data – Connecting Parts of the Donut to Each Other with Lines
One of the reasons pie charts are helpful is that we can identify patterns in data by connecting parts of the pie chart to each other with lines. For example, the below figure has one whole pie chart and two small, partial pies. Our brains recognize the larger pie chart and infer a pattern between it and the smaller pies to figure out that they share something in common. What do they have in common? They both represent populations on either side of a border who want to become US citizens but need a visa to do so. When you see one or more segments of your data represented as a partial slice, draw connections back to the full view or some other segment to help you understand what’s being shown.
Conclusion
Pie charts are one of the most common types of charts used to show data, and they’re often used when you have one category that accounts for the majority of the data points you want to present, and two or more other categories that make up the rest of the data points.
