What Is a Bubble Chart?

Key takeaways

• A bubble chart is a type of graph that displays data as circles, making it easy to see relationships among three, and sometimes even four, variables.

• A bubble chart is used to help you make in-depth comparisons to improve decision-making, identify trends, prioritize projects, evaluate investment portfolios, and track organizational performance, among other things.

• One advantage of a bubble chart is that it makes it easy to display large amounts of information, although a disadvantage of bubble charts is that they can make it difficult to determine exact values.

To create an effective bubble chart, use appropriate and accurate data, include only the most relevant data to avoid overcrowding, employ design elements to enhance readability, and include a legend to help viewers interpret your chart. Continue reading to learn when to use bubble charts, how to weigh the pros and cons, and tips for reading this type of graphic.

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What is a bubble chart?

A bubble chart is a type of data visualization that displays information as circles (bubbles). You can use bubble charts to combine three or, more rarely, four different types of information into one chart. In this type of graph, you use differently sized bubbles positioned along the x-axis and y-axis to represent your variables. In some cases, you may also use the color of the bubble to represent a category or group.

For example, your x-axis might represent time of day, your y-axis might represent call volume, and your bubble size might represent how many people work in the call center. If you saw a large bubble positioned low on the y-axis, it would indicate that a high number of people were working at the call center during a period of low call volume. If you saw a small bubble high on the y-axis, you would see that a low number of people were working during a time with a high volume of calls. The x-axis values indicate when each scenario occurred during the day. Based on information like this, you could redistribute your workers so that an appropriate number of people are working based on how busy the call center is at any given time.

Bubble chart vs. scatter plot

A bubble chart and a scatter plot both show relationships between variables, but they differ in the amount of data they represent. A scatter plot displays two variables using points positioned along the x- and y-axes. This can show trends within the data, correlations between the x and y variables, and help you spot outliers.

A bubble chart, on the other hand, adds a third variable, which is shown by the size of the bubbles. This visualization allows you to make more in-depth comparisons and provide additional information that may be relevant for decision-making.

What is a bubble chart used for?

Use a bubble chart when you need to display relationships among three variables in a visually engaging way. For instance, if you want to compare companies based on revenue (x-axis), customer satisfaction (y-axis), and market share (bubble size), a bubble chart can show all of this information clearly in one place. Using bubble charts, you can reveal trends you might not have seen before and tell a story with your data, making it easier for you and your stakeholders to understand. Bubble charts can be a good choice if your goal is to display a large amount of information simply and effectively.

Read more: What Are the Top Data Visualization Techniques?

What types of professionals use bubble charts?

Professionals of all types can use bubble charts to represent the relationship between several types of variables, but you might see it more commonly used by business professionals. Bubble charts are a great way to visualize and compare relationships among variables such as cost, revenue, risk, and value.

As a business professional, you might use a bubble chart to identify the most profitable customer type for your product or service by examining the relationships among acquisition cost, customer service engagement, and revenue for each customer. You might also group them by color to find additional trends. You could also prioritize projects based on cost, expected time, and estimated revenue to determine which projects carry the most value. Other examples might include evaluating an investment portfolio, comparing campaign metrics, identifying employee satisfaction drivers, and tracking organizational performance.

What is a bubble diagram?

A bubble diagram is a drawing, often by hand and used in architecture, that uses bubbles to represent spaces and lines to show their relationships. Like bubble charts, bubble diagrams are used for visualization and to aid decision-making by providing a rough sense of the flow of space, which can help in developing a more refined plan. The bubbles in a bubble diagram can vary in size and shape to better represent different kinds of spaces.

Advantages and disadvantages

Bubble charts are an effective and visually appealing way to display the relationship between several variables simultaneously. However, it’s important to be aware of this tool's strengths and weaknesses to ensure you use it appropriately and accurately.

What are the advantages of bubble charts?

Advantages of using a bubble chart to create a visualization of your data include the option to show time-based changes and display large volumes of data, especially when you have more than two variables.

• Easy to display large volumes of information: Because bubble charts can represent three to four types of information, you can display a high volume of information in a relatively simple visualization.

• Able to effectively compare two data sets: By color-coding the bubbles, you can use bubble charts to compare how the relationship between different variables differs between several groups.

• Can show time-based changes: By using the x-axis as a time variable, you can see how certain variables change over time and track trends.

What are the disadvantages of bubble charts?

When precision is key, or when thoughtful sizing and positioning of your bubbles are not possible, you may want to choose another type of visualization. Another disadvantage of bubble charts is that they may be less effective for variables other than continuous ones.

• Best suited to continuous variables: If one of your variables represents only one entry in a given category, another type of visualization may be better.

• Design flaws can limit utility: If you have too many bubbles or are not thoughtful about how you position, size, and sort your data, your visualization may be ineffective.

• Not ideal for showing exact values: The size of the bubbles represents data relative to one another, making it difficult to determine the exact value from the bubble.

How do you make a bubble chart? Tips to create an effective visualization

Choosing your data is one of the most important aspects of designing your visualization to create the most effective bubble chart. By using appropriate and accurate data, you can create clearer graphs that depict the relationship between variables without obscuring the overall message. Be sure to use continuous variables for your x-axis, y-axis, and bubble size, and a grouping variable for color if you choose.

Display only the most important data points to prevent overcrowding. If you use too many bubbles, your chart might be hard to read and interpret, so focus on the key data that adds value. This also helps to keep your chart clear and simple. You can employ design elements to improve your readability if needed. For example, you might use transparency to manage overlapping bubbles and avoid unnecessary elements that might distract from the main message.

Another thing to consider is the legend or key. Make sure to include a legend that explains what the bubble sizes represent and any colors you use to differentiate categories or groups. This ensures viewers can easily interpret the chart. Regarding bubble size, accurate scaling is also important to avoid distorting the data.

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