Choosing the right chart type: Line charts vs Area charts

The Line and the Area chart  look very similar. They even facilitate the same kind of analysis yet they cannot be used interchangeably.

A line chart connects discrete but continuous data points by using straight line segments. It is effective in facilitating trend analysis.

Example of line chart facilitating trend analysis

An area chart does the same except that the area below the plotted line is filled with color.

Example of area chart

Let’s see the optimum use of both these charts

When there are multiple data sets

Line charts can easily be used to display multiple data sets.

Line chart with multiple data sets

However, in  Area charts, we cannot show multiple data sets clearly as the upper layer hides the layers below (occlusion).

Area chart with many data sets (occlusion)

The problem of occlusion, can be minimized by increasing the transparency of the different layers but nonetheless it still persists.

Area chart with many data sets in transparent layers

Increasing the transparency works best up to two data sets.

Area chart with two data sets

When area under the plotted line represents a summation

Let’s say you visualize your Revenue Vs Expenses data using an Area chart.

Area chart summation

From this chart, we can get an approximate idea of the profits for the period by visually subtracting the expenses from the revenue.

Line chart summation is not possible

In a Line chart, there is no visual element (such as colored area) to support such cognitive relationships.

When you want to establish part-to-whole relationship

Similar to a Stacked column chart, a Stacked area chart displays part-to-whole relations by showing the constituent parts of a whole one over the other.

Let’s say you want to visualize your region-wise sales.

Stacked area chart

Using a Stacked area chart, you can not only get an idea of the total sales for a month but also the contribution of each region. It is however, difficult to interpret the area of each region precisely as the height of each region is affected by the pattern below it.

On the other hand, a Line chart is more effective in facilitating an understanding of the trend of your monthly region-wise sales.

Line chart trend analysis

The trend for the total sales however, have to be obtained manually (by adding the monthly region-wise values and then plotting it as a separate line).

Line chart with trend and total

A user in hurry  may however, misinterpret the total sales line as another regional sales line, if he/she does not refer the chart legend. To avoid this, make your total sales line visually distinct from the regional sales lines.

Line chart with distinct total sales

To sum up, while both the Line and the Area charts can be used to facilitate trend analysis, it is better to use the Area chart when there is a summation relationship between the data sets or when you want to show part-to-whole relationship (along with trend).

Keep watching this space for more insights on charting best practices.

Happy charting till next time 🙂

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