Data Visualization 101: Area Charts

In our Data Visualization 101 series, we cover each chart type to help you sharpen your data visualization skills.

Like the mountains that they resemble, area charts are a representation of change over time. Whether you’re looking to chart net earnings for individual departments month to month or examining the popularity of music genres since the ‘50s, there are few chart types that communicate time-series relationships so well. Let’s see how area charts can work for you.

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Google’s music timeline uses an area chart to show the popularity of difference genres:

music timeline

What’s an Area Chart?

Area charts depict a time-series relationship. But unlike line charts, they can also visually represent volume. Information is graphed on two axes, using data points connected by line segments. The area between the axis and this line is commonly emphasized with color or shading for legibility. Most often area charts compare two or more categories.

The History

If you’ve read the other installments in this series, you’ll know William Playfair was a major innovator in data visualization, inventing the pie chart, the bar chart, and, yes, the area chart.

The “Commercial and Political Atlas of 1786” featured the first area chart:

playfair-visualization-national-debt-line-graph

When to Use an Area Chart

Area charts are perfect when communicating the overall trend, as opposed to the individual values. Use a stacked area chart for multiple data series with part-to-whole relationships or for cumulative series of values.

There are three main variations on this chart, and each has its best use, depending on the situation.

Standard Area Chart: This is best used to show or compare a quantitative progression over time. In cases where many data series are to be graphed, a line chart is usually a more legible choice. (See the solution for hidden data points in our design tips below.)

standard area chart

Stacked Area Chart: This is best used to visualize part-to-whole relationships, helping show how each category contributes to the cumulative total.

stacked area chart

100% Stacked Area Chart: This is best used to show distribution of categories as parts of a whole, where the cumulative total is unimportant.

100 stacked area chart

Tips for Creating Area Charts

Area charts are increasingly popular, but without proper design they can be difficult to decipher. Make sure you are always following best practices.

1. Make It Easy to Read

In stacked area charts, arrange data to position categories with highly variable data on the top of the chart and low variability on the bottom.

easy to read 1

2. Use Transparent Colors

In standard area charts, ensure data isn’t obscured in the background. Order thoughtfully and use transparency.

Use Transparent Colors

3. Start Y-Axis Value at 0

Starting the axis above zero truncates the visualization of values.

start at zero

Want more? Read up on the pie chart, bar chart, and line chart.

And for more on how to design your data, download the free e-book from our friends at Visage (where this post appeared first):

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(Lead image modified from original by Dawn Endico)

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