![]() Viewers can’t always be sure what each series is using as a baseline value More likely, at least once in your chart you’ll see data series cross over one another, and then you will inevitably have hidden data. The BEST case scenario is that your data series never cross over one another, so that the chart looks like a mountain range where all peaks are visible. In most cases, some of your information will be hiddenīecause your data series occupy the same space in your graph, they will inevitably overlap. As such, it’s only natural that area graphs have a few drawbacks. This particular chart type combines qualities of such controversial visualizations as bubble charts (comparing by area), stacked bar charts (comparing subcategories across categories), and scatterplots (allowing some data to be hidden behind other data), while encouraging the use of color as a categorical differentiator instead of a tool for focusing attention. Shading the region between the lines can emphasize that gap. They can also be useful if you are trying to show the gap between two (and only two) series, or between a series and 100% and that gap is more important than the absolute value between the lines. Showing the difference between two series, or between a series and 100% Where the data series overlap, however, it can be challenging for the audience to read that two (or more) fills are occupying the same space.Ĭontinuing with the same example we have been using, which shows inflation-adjusted sales of music by format over time, we attempt to mitigate this challenge with a small change to the opacity of our “fill” colors, as shown below. The area graph attempts to give a sense of quantity over all points of time, by creating irregular polygons of filled color. The chart gets crowded and cluttered very quickly. Bar charts are good at showing a quantity at one point in time, but multiple series across multiple points in time are challenging to show as bars. Sometimes, it’s important to show how quantities have changed over time across multiple related data series. Showing several series, across several different time periods, if there is significant variation among series and change over time Still, here are a few cases for which the area graph might be a reasonable option. We rarely ( but not never!) find ideal use cases for the area graph. As we discussed earlier, however, line graphs and area graphs are not interchangeable, due to how viewers perceive the different presentations of data. They are colorful, eye-catching, and are uncommon enough that the novelty factor tends to draw attention. Also, just like with bar charts, we must use a zero baseline.Īrea graphs are tempting to use in lieu of line graphs. Instead of seeing lines, we see each data series as a polygon, as a shape and we judge each data series less by how it changes over time, and more by what we perceive the overall area of the colored region to be.Īn area graph transforms the purpose of the line graph from simply showing relative change over time to additionally showing volume or quantity as well.įor that reason, we can’t use scales on area graphs that don’t have a meaningful relationship to zero. ![]() Here’s a line graph of music sales over time in the U.S., broken down by format: The space between the x-axis and each line in the graph is filled with some color (possibly of varying hue or opacity, depending on the designer’s preference). ![]() In this post, we’ll talk about how an area graph works, and some of the challenges to keep in mind when you are considering creating one.Īrea graphs are the same as a regular line graph, with two exceptions: Showing several volatile data sets over time Showing change over time in individual panels of a small multiple chartĪrea graphs are not the ideal choice for:ĭata sets on scales that do not have a meaningful relationship to zero Showing the rise and fall of various data series over timeĬonveying total amounts over time as well as some sub-categorical breakdowns (but only to a point)Įmphasizing a part-to-whole relationship over time when one part is very large, or changes from being very large to very small This might seem to be a minor cosmetic change, but it has a significant effect on how we perceive the data in the chart. An area graph is a specialized form of the line graph, where instead of simply connecting our data points with a continuous line, we also fill in the region below that line with a solid color.
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