At Chartio, we often see questions from people around how to best display data for effect. One question, in particular, is often asked: “When should I use a bar or line chart?”
To answer that question, it’s best to first understand how we want to visualize our data. Generally, data falls into two types of camps: continuous or categorical. Continuous data is data that can be measured (ie. time, revenue, amount). Categorical data, on the hand, is data that can be distinguished into different groups (ie. product type, gender, country)
Knowing this, how do these different types of data factor into which chart to use?
Bar Charts: Bar charts are best used for categorical data. They are typically used to compare different groups (ie. comparing marketing channel performance, or sales by product), though in some occasions can be used on continuous data, like tracking changes over time. Bar charts, unlike line charts, do not require a continual relationship between points (unlike time or a sequence of steps).
Line Charts: Line charts are used to track changes over periods of time (chronological) or in a sequence (ie. dates, months, stages, steps). Line charts are used primarily to detect trends and patterns as opposed to giving its viewers exact numbers.
Since both bar charts and line charts can actually be used to denote continuous data (like performance over time), it’s important to understand how you can use them for the greatest effect. Bar charts are useful to better emphasize major changes between time periods, whereas line charts are useful to highlight ongoing trends over time.
Bar and line charts are some of the most common visualizations used in analysis, and are very helpful in allowing people to easily see what their data is telling them. By effectively choosing between bar and line charts, you can quickly help your readers understand what it is they are looking at.