Data visualizations don’t need to be complex to communicate your message. Bar and line charts are two effective options for illustrating business changes at data-driven organizations. As Computer Science Professor Ben Schneiderman explains, “the purpose of visualization is insight, not pictures.” When choosing between bar and line charts, it’s important to understand their unique benefits.
What Are the Best Applications of Bar Charts and Line Graphs?
As visualization blogger Drew Skau highlights, a line chart best shows a continuous series of data, like temperature or time. Bar charts, on the other hand, can display continuous data, but they can also be used to display categories of data. To understand the difference between continuous and categorical data, ask yourself: Is there more than one category of data? If the answer is no, the data set is continuous.
If you’re using a single category, such as days of the week, a line chart should be the right choice. In the header example, the line chart shows a progression of inquiries about Santa over the 7 days before Christmas by two different groups – kids who behaved all year and kids who didn’t. Comparing this data in a bar chart would be possible, but not as effective because the bars would be unable to show the progression as clearly.
If you’re using different categories, such as types of food consumed by two different groups, a bar chart will be more effective. In the header example, the categories (vegetables, carbs, fruit) have no relation with progression over time, and the data in each category (comparing kid and adult consumption) stands as an individually worthwhile comparison as well as a relevant comparison within the larger set of data (all three food types together). The visual separation between bars allows viewers to create mental barriers between different data categories, which aids in comparing the data on multiple levels.
In addition to considering whether you are graphing categorical vs. continuous data, a few additional factors can determine whether bar charts or line charts are best. Consider the following factors when selecting the right mode of display for simple visualizations:
- Are Your Changes Significant? Line charts are better at showing slight changes in data, while bar charts are best for highlighting significant changes. Sometimes you may need to graph your data in both a line and a bar chart to determine which format is easiest to understand.
- How Many Data Sets Am I Displaying? Graphing several sets of data on a single chart is always challenging; however, line charts with multiple lines can be a more effective means of charting changes in several data sets over time. Line charts could be superior because they naturally contain more visual white space, which is less overwhelming to viewers.
Regardless of the chart type you select, the visualization should communicate your message simply and clearly. Selecting the wrong chart type or committing other errors like poor graph scale can be confusing to the viewer. The best visualizations are immediately clear and convey an accurate message.