A bubble chart is a variation of a scatter plot that displays data points as bubbles.
A bubble chart consists of a series of values that are plotted on an x-axis and y-axis, with each axis representing a variable and each value represented as a dot. The third variable value is then used to proportionally scale each bubble or dot. Bubble charts often include an independent variable, such as years of education, a dependent variable, such as annual income, and a proportional variable, such as population. When the dots are plotted against these two axes, bubble charts communicate the strength, type, and proportion of the relationship that exists between these variables.
Always include a legend if more than one category of data is being visualized.
Always ensure that smaller dots are visible when overlapping with larger dots.
- Either by placing smaller dots above larger dots or by making the larger dots transparent.
Never let larger values obscure smaller values.
Never use symbols for point markers that do not have a proportionate width and height.
- A symbol that has an equal width and height is a more accurate way to present a given data value.
Never include more than 3 sets of values in a static bubble chart.
It is recommended that the title explain the unit of analysis.
It is recommended that you include point labels or markers for specific observations.
It is not recommended to use a bubble chart if there are an excessive number of values that result in the dots appearing illegible.