When deciding between using a bar or a line chart for data visualization, understand what you are visualizing. Generally, data falls into two groups:
- Categorical data: data that is distributed into different groups (eg. product type, gender, country, etc.).
- Continuous data: data that can be measured (eg. time, revenue, amount).
Bar charts are best used for categorical data. They are usually used for comparing different groups, for example, comparing marketing channel performance, though in some occasions can be used on continuous data, such as tracking changes overtime. Bar charts, unlike line charts, do not require a continual relationship between points (unlike time or a sequence of steps).
Line charts are used to track changes over periods of time (chronological) or in a sequence (eg. dates, month, stages, etc.). Line charts are supposed to detect trends and patterns as opposed to giving its viewers exact numbers, making them most useful to highlight ongoing trends over time.