Using Pie and Donut Charts Effectively: A Detailed Guide
Pie and donut charts are popular data visualization tools that show how a whole is divided into different parts or categories. These charts are effective for illustrating the relative proportions of categories within a dataset. While pie and donut charts share a similar structure, the donut chart offers some design flexibility by removing the center of the pie. However, both charts are often used interchangeably.
This detailed guide will walk you through the purpose, types, design considerations, best practices, and practical use cases of pie and donut charts.
1. Understanding Pie and Donut Charts
1.1 Pie Chart
A pie chart is a circular graph that is divided into sectors (or slices), where each sector represents a portion of the total. The area of each sector is proportional to the quantity it represents, making it easy to compare parts of a whole visually.
- Use Cases:
- Displaying the percentage breakdown of a whole (e.g., market share of companies).
- Showing the composition of a category (e.g., expenditure distribution).
- Comparing parts to the whole in a way that’s simple and easy to understand.
- Components:
- Sectors (Slices): Each slice represents a category, with its size relative to the percentage or value it represents.
- Labels: Labels or data values are typically shown on or near the slices, indicating the percentage or value of each category.
- Legend: Optional legend showing color representations for each category.
1.2 Donut Chart
A donut chart is a variation of the pie chart where the center of the pie is removed, leaving a “donut” shape. This design creates a visually appealing chart with more space in the center, often used to display additional information or make the chart less cluttered.
- Use Cases:
- Showing proportions of a whole with additional central space for labels, titles, or summary information.
- Displaying data where the emphasis is on the percentage contribution of different categories.
- Enhancing pie charts by making them easier to read, especially when there are many small segments.
- Components:
- Outer Ring: Like the pie chart’s sectors, this outer ring represents data categories and their proportions.
- Center Hole: The hole in the center of the donut chart provides space for additional text, titles, or to make the chart more aesthetically pleasing.
- Labels: Labels for each segment or central data annotations.
2. Designing Pie and Donut Charts
Effective pie and donut charts require attention to detail to make sure they communicate the data clearly and do not overwhelm the viewer. Here’s how to design them effectively:
2.1 Choosing the Right Chart Type
- Pie Charts: Choose a pie chart when:
- You have a small number of categories.
- You want to show simple, straightforward data and how parts contribute to the whole.
- The focus is on the relative proportions of the categories.
- Donut Charts: Choose a donut chart when:
- You want to emphasize the breakdown of a whole but also require some space in the center for additional information.
- You need a more visually appealing chart, with a cleaner look by eliminating the center.
- You have a need to display multiple categories while keeping the design less cluttered.
2.2 Handling Multiple Categories
- Limit the Number of Slices: Both pie and donut charts become harder to interpret as the number of slices increases. Generally, try to limit the chart to 5–7 categories. If you have more than that, consider grouping smaller categories into an “Others” slice.
- Color Scheme: Use a consistent color scheme for your slices. Use distinct colors for each category to avoid confusion. Choose colors with sufficient contrast to make the chart readable. Avoid using too many similar colors as it can make the chart look cluttered.
2.3 Labeling Slices
- Percentage or Value Labels: Display percentages or actual values in or near the slices. For pie charts, labels should be placed in a way that they don’t overlap or cause confusion.
- Avoid Overcrowding: Keep the labels short and clear to ensure they don’t clutter the chart. If necessary, use tooltips or a legend to display additional details.
- Positioning Labels: In donut charts, labels are often placed either inside the segments or outside the donut. Inside the donut, labels can be positioned closer to the center, making them more readable.
2.4 Spacing Between Slices
- Pie and donut charts can sometimes become difficult to interpret when slices are too close to each other. Consider providing a small gap between the slices to make each segment more distinct. This can be done by adjusting the inner radius in donut charts.
2.5 Adding Central Text (for Donut Charts)
- The center of a donut chart can be used to provide key insights, such as the total value, the percentage of a specific category, or additional annotations. This can help add more context to the chart and improve understanding.
3. Best Practices for Using Pie and Donut Charts
3.1 Limit the Number of Categories
Avoid pie and donut charts with too many slices. As the number of categories increases, the chart becomes harder to interpret. Aim for no more than five to six slices. If necessary, combine smaller categories into an “Others” slice or represent the data in a different chart type (e.g., bar or column chart).
3.2 Use Legends or Tooltips
When you have multiple categories, it’s often better to include a legend or use tooltips to identify each slice. This ensures that the chart remains readable even when you need to represent several categories.
3.3 Emphasize Key Slices
To emphasize certain slices, use highlighting techniques such as bold colors, larger slices, or contrasting labels. This can draw attention to key data points you want to highlight, such as the largest segment.
3.4 Avoid Pie Charts for Precise Comparisons
Pie charts are great for showing proportions, but they aren’t ideal for precise comparisons between categories. For small differences, it’s often better to use bar or column charts, where exact values are more easily compared.
3.5 Use Donut Charts for Aesthetic Appeal
Donut charts can be more visually appealing and less cluttered than pie charts, especially when you want to place additional information (e.g., total value or key insights) in the center of the donut. Use donut charts when the aesthetic or design of the chart is important.
3.6 Percentage Labels and Formatting
When using percentages in pie and donut charts, ensure the percentage labels are legible. Avoid displaying too many decimal places; typically, one or two decimal points are sufficient. For better readability, format the labels as percentages (e.g., “25%” rather than “0.25”).
4. Practical Examples of Using Pie and Donut Charts
4.1 Market Share Analysis
A pie chart is an excellent choice when comparing the market share of different companies. For instance, you can display the percentage of market share held by each company in a particular industry.
- Design Tip: Keep the chart simple with up to 5 or 6 companies. Label each slice with both the percentage and the company name.
4.2 Budget Breakdown
Donut charts are useful for visualizing budget allocations. The center space can be used to show the total budget amount, while the donut’s outer ring can represent the proportions of different budget categories, such as marketing, operations, and salaries.
- Design Tip: Use color-coding for each budget category and ensure the total budget value is clearly labeled in the center.
4.3 Survey Results
For survey results where respondents select from a list of options (e.g., “What’s your favorite color?”), a pie chart can be used to show the relative proportions of each response.
- Design Tip: Add a legend to indicate the responses, and use a consistent color scheme to represent each option.
4.4 Composition of a Product or Service
A donut chart can represent the composition of a product or service, such as a breakdown of ingredients in a food product or features in a software tool.
- Design Tip: Highlight the most important ingredients or features by making them larger or a different color.
5. Interpreting Pie and Donut Charts
When interpreting pie and donut charts, keep the following points in mind:
- Relative Size: Look at the size of each slice to understand its proportion compared to the whole. A larger slice indicates a more significant share of the total.
- Label Accuracy: Ensure that labels and percentages are correctly displayed and easily readable.
- Outliers: Be cautious about slices that seem disproportionately large or small. Investigate whether these slices represent extreme cases, errors, or important data points.
- Proportions: Remember that pie and donut charts are useful for showing proportions but less effective for showing exact numbers or comparisons between multiple data points.
Conclusion
Pie and donut charts are powerful tools for showing how parts make up a whole, making them perfect for representing data with categorical breakdowns. However, they require careful design to ensure the information is easy to understand and visually appealing. By following best practices such as limiting the number of categories, labeling clearly, and using the right chart type for the data, you can create effective pie and donut charts that communicate insights clearly and effectively.