The Line and the Area chart look very similar. They even facilitate the same kind of analysis yet they cannot be used interchangeably.
When to Use Line Chart vs Area Chart
Line charts are usually for observing trends over a certain period of time. The Y axis shows numeric values and the X axis represents the key measurements. Line charts are clear and easy to understand since you can see the specific trend for the individual data group.
Area charts have a pattern similar to line charts. However, the space between each line and the X-axis is filled with a certain color. Area charts are ideal for indicating a change among different data sets.
A line chart connects discrete but continuous data points by using straight line segments. It is effective in facilitating trend analysis. An example of the application of line charts in real life is by financial managers to check trend for profits and other business factors.
An area chart does the same except that the area below the plotted line is filled with color.
Let’s understand the scenarios where these charts shine through in their own right.
When there are multiple data sets
Line charts can easily be used to display multiple data sets.
However, in area charts, we cannot show multiple data sets clearly as the upper layer hides the layers below (occlusion). This becomes especially bad when you have more than two data categories.
The problem of occlusion can be minimized by increasing the transparency of the different layers, but nonetheless it persists.
Increasing the transparency works best up to 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.
From this chart, we can get an approximate idea of the profits for the period by visually subtracting the expenses from the revenue.
In a line chart, there is no visual element (a 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 sales per region.
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.
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).
There is room for misinterpretation of the total sales line as another regional sales line, if the user does not refer the chart legend. To avoid this, make your total sales line visually distinct from the regional sales lines.
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).
For more insights on charting best practices, check out this space.