Pie and donut charts in Power BI - Deep Dive

Overview - Pie and donut charts

What is it?

Pie and donut charts are circular charts used to show how parts make up a whole. Each slice or segment represents a category's proportion compared to the total. Donut charts are like pie charts but have a hole in the center, which can be used to display additional information. They help people quickly see the size of categories relative to each other.

Why it matters

These charts exist to make it easy to understand proportions and percentages at a glance. Without them, it would be harder to compare parts of a whole visually, especially for non-technical users. They simplify complex data into a familiar shape, helping decision-makers spot trends and imbalances quickly.

Where it fits

Before learning pie and donut charts, you should understand basic data visualization concepts like charts and categories. After mastering these, you can explore more advanced visualizations like bar charts, stacked charts, and interactive dashboards to analyze data deeper.

Mental Model

Core Idea

Pie and donut charts show how different parts share a whole by dividing a circle into slices sized by their proportion.

Think of it like...

Imagine cutting a pizza into slices where each slice size shows how many people want that topping. The bigger the slice, the more popular the topping.

┌───────────────┐
│     Pie       │
│   Chart       │
│   (Circle)    │
│   ┌───────┐   │
│   │ Slice │   │
│   │  25%  │   │
│   └───────┘   │
│   ┌───────┐   │
│   │ Slice │   │
│   │  75%  │   │
│   └───────┘   │
└───────────────┘

Donut Chart:

┌───────────────┐
│   Donut       │
│   Chart       │
│  (Circle with │
│   hole inside)│
│   ┌───────┐   │
│   │ Slice │   │
│   │  40%  │   │
│   └───────┘   │
│   ┌───────┐   │
│   │ Slice │   │
│   │  60%  │   │
│   └───────┘   │
└───────────────┘

Build-Up - 6 Steps

1

Foundation

Understanding parts of a pie chart

Concept: Learn what slices represent and how they relate to the whole.

A pie chart is a circle divided into slices. Each slice shows a category's share of the total. For example, if you have sales data for three products, each slice shows how much each product contributes to total sales. The size of each slice is proportional to its value compared to the total sum.

Result

You can see which category is largest or smallest by looking at slice sizes.

Understanding that pie slices represent parts of a whole helps you grasp why pie charts are useful for showing proportions.

2

Foundation

Difference between pie and donut charts

Concept: Recognize the visual and functional difference between pie and donut charts.

A donut chart looks like a pie chart but has a hole in the center. This hole can be used to display extra information, like the total value or a label. The slices still represent parts of the whole, but the donut shape can make it easier to read or add context.

Result

You can choose donut charts when you want to add center labels or reduce visual clutter.

Knowing the difference helps you pick the right chart type for your message and design needs.

3

Intermediate

Creating pie charts in Power BI

🤔Before reading on: do you think you need to prepare data differently for pie charts than for tables? Commit to your answer.

Concept: Learn how to build a pie chart using Power BI's interface and data fields.

In Power BI, to create a pie chart, drag a categorical field to the 'Legend' area and a numeric field to the 'Values' area. Power BI automatically calculates the proportion of each category. You can customize colors, labels, and tooltips to improve clarity.

Result

A pie chart appears showing slices sized by category values.

Understanding how Power BI maps data fields to chart parts helps you create meaningful visualizations quickly.

4

Intermediate

When to avoid pie charts

🤔Before reading on: do you think pie charts work well with many categories or very small slices? Commit to your answer.

Concept: Learn the limitations of pie charts and when they become hard to read.

Pie charts become confusing when there are too many slices or when slices are very small and similar in size. It’s hard to compare small slices visually. In such cases, bar charts or stacked charts are better choices.

Result

You avoid creating misleading or cluttered pie charts.

Knowing pie chart limits prevents poor data communication and helps you choose better visuals.

5

Advanced

Using donut charts for center metrics

🤔Before reading on: do you think the hole in donut charts is just decorative or can it hold useful info? Commit to your answer.

Concept: Learn how to use the center space in donut charts to display key metrics or labels.

In Power BI, you can add a card or text box over the donut chart’s center to show total values or important messages. This adds context without cluttering the slices. It helps viewers understand the whole while seeing parts.

Result

Donut charts become more informative and visually balanced.

Using the center space effectively enhances the chart’s storytelling power.

6

Expert

Customizing pie/donut charts for accessibility

🤔Before reading on: do you think color alone is enough to distinguish slices for all users? Commit to your answer.

Concept: Learn how to design pie and donut charts that are accessible to people with color blindness or other visual impairments.

Use patterns, labels, and high-contrast colors instead of relying only on color differences. Power BI allows data labels and tooltips to improve clarity. Also, ensure keyboard navigation and screen reader support by adding descriptive titles and alt text.

Result

Charts are understandable by a wider audience, including those with visual challenges.

Accessibility-aware design ensures your insights reach everyone, not just those with perfect vision.

Under the Hood

Pie and donut charts work by calculating each category's value as a fraction of the total sum. The chart engine converts these fractions into angles for slices, where 100% equals 360 degrees. The rendering engine draws each slice as a sector of the circle. Donut charts add a circular mask in the center to create the hole. Labels and colors are layered on top for clarity.

Why designed this way?

The circular shape was chosen because humans naturally understand circles and angles as parts of a whole. The donut hole was introduced to reduce clutter and provide space for additional information. Alternatives like bar charts show parts but lack the intuitive 'whole' shape. Pie charts have been used historically for their simplicity and immediate visual impact.

Data Values → Calculate Fractions → Convert to Angles → Draw Circle Slices

┌───────────────┐
│   Data Input  │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Calculate %   │
│ of Total      │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Convert to    │
│ Angles (°)    │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Render Slices │
│ on Circle     │
└──────┬────────┘
       │
       ▼
┌───────────────┐
│ Add Labels &  │
│ Colors        │
└───────────────┘

Myth Busters - 4 Common Misconceptions

Quick: Do you think pie charts are always the best way to show parts of a whole? Commit yes or no.

Common Belief: Pie charts are the best and simplest way to show any part-to-whole data.

Reality: Pie charts are only effective with a few categories and clear size differences. With many categories or similar sizes, they become confusing.

Why it matters: Using pie charts in wrong situations leads to misinterpretation and poor decisions because viewers can't accurately compare slices.

Quick: Do you think donut charts are just pie charts with a hole and nothing more? Commit yes or no.

Common Belief: Donut charts are just decorative pie charts with no added value.

Reality: Donut charts provide useful center space for totals or labels, improving clarity and context.

Why it matters: Ignoring the center space wastes an opportunity to communicate key information effectively.

Quick: Do you think color alone is enough to distinguish slices for all viewers? Commit yes or no.

Common Belief: Using different colors for slices is enough for everyone to understand the chart.

Reality: Color alone can be problematic for color-blind users or in poor lighting. Patterns and labels are needed for accessibility.

Why it matters: Relying only on color excludes some viewers and reduces the chart's effectiveness.

Quick: Do you think pie charts can accurately show negative or zero values? Commit yes or no.

Common Belief: Pie charts can display negative or zero values just like positive ones.

Reality: Pie charts cannot represent negative or zero values because slices represent parts of a whole and must be positive.

Why it matters: Trying to use pie charts with negative data leads to confusion and incorrect visuals.

Expert Zone

1

Small slice aggregation: Experts often group very small slices into an 'Other' category to keep pie charts readable.

2

Angle perception bias: Humans perceive angles differently than areas, so slice size perception can be misleading; experts compensate by adding data labels.

3

Center label dynamics: In donut charts, dynamically updating the center label based on user interaction improves storytelling and engagement.

When NOT to use

Avoid pie and donut charts when you have many categories, very small differences, or need to show trends over time. Instead, use bar charts, stacked bar charts, or line charts for clearer comparisons and temporal analysis.

Production Patterns

In real dashboards, pie and donut charts are used for high-level summaries like market share or budget allocation. They are often combined with filters and tooltips for interactivity. Experts customize colors for brand consistency and add center labels in donut charts to highlight totals or key metrics.

Connections

Bar charts

Alternative visualization for part-to-whole data

Knowing when to use bar charts instead of pie charts helps avoid misinterpretation and improves clarity for many categories.

Gestalt principles of visual perception

Builds-on visual grouping and figure-ground concepts

Understanding how people perceive shapes and colors explains why pie charts work well for showing wholes and parts.

Human color vision and accessibility

Opposite domain but critical for design choices

Knowing how color blindness affects perception guides better chart design for inclusivity.

Common Pitfalls

#1 Using pie charts with too many categories causing clutter.

Wrong approach:

Create a pie chart with 15 categories, each with small slices, without grouping.

Correct approach:

Group small categories into 'Other' to reduce slice count before creating the pie chart.

Root cause:

Misunderstanding that pie charts become unreadable with many small slices.

#2 Relying only on color differences to distinguish slices.

Wrong approach:

Use similar shades of blue for multiple slices without labels or patterns.

Correct approach:

Use distinct colors, add data labels, and consider patterns for accessibility.

Root cause:

Assuming color alone is sufficient for all viewers.

#3 Trying to show negative values in pie charts.

Wrong approach:

Include negative sales values as slices in a pie chart.

Correct approach:

Exclude negative values or use a different chart type like bar chart.

Root cause:

Not knowing pie charts require positive parts of a whole.

Key Takeaways

Pie and donut charts visually represent parts of a whole using slices sized by proportion.

Donut charts add a center hole that can display extra information, improving clarity.

These charts work best with few categories and clear size differences to avoid confusion.

Accessibility requires more than color differences; labels and patterns help all users understand.

Choosing the right chart type depends on data characteristics and the story you want to tell.