- Use a chart when the user will need to detect overall patterns from one or more datasets, or the relationships between those datasets.
- Select a chart type that works for the type of data being visualized. With a time series, for example, a line chart will work well, with time displayed on the x-axis, whereas the vertical arrangement of bars in a horizontal bar chart will not.
- Don’t use a chart when the primary purpose is for the user to compare numerous specific values. Consider using a data table instead.
- Don’t use a single chart to display data from more than 4 series at a time, because the chart will become difficult to decipher, particularly on smaller devices.
Horizontal bar charts
These charts display horizontal bars aligned to the y-axis. The bars are used to represent discrete quantities or amounts.
Compared with column charts (see below), horizontal bar charts have more space available for their item labels, so they’re great for visualizing discrete values when data labels are long (for example, product names).
- Use to represent measurements for discrete items.
- Use for items that have long label names, because the y-axis labels can expand.
- Don’t use to display time-based data, because time values are usually demarcated from left-to-right along the x-axis, but here the x-axis is used to show the value of each chart item.
These charts use vertical bars to represent quantities and amounts. With their side-by-side arrangement of columns, they can be used to illustrate changes in values over time. The horizontal spacing between each column (or cluster) serves to reinforce the distinctness of each chart item or group. Please note that the y-axis baseline always starts at 0, with positive values appearing above and negative values below.
- Use for comparing values from non-time series datasets.
- Can be used instead of a line chart for time series data when it is either 1) more important to see the value of each item than the overall shape of the data or 2) the dataset is missing values which would create gaps in a line chart.
- Don’t use with extremely large data sets, because the columns will be too narrow to accurately differentiate or easily select; use a line chart instead.
- Don’t use when the x-axis labels become truncated; use a horizontal bar chart instead (only for non-time series datasets).
Line charts use straight lines connecting points plotted in 2-D space to represent data and trends. They are useful for showing the change in values (continuous or discrete) over time.
- Use to display a trend in the data, because the connections between the datapoints provides an overall shape to the dataset.
- Don’t use for data sets when the values along the x-axis are unrelated, because the line may imply a trend that does not exist.
- Don’t use when the dataset is missing several values, because breaks will appear in the line; use a column chart instead.
Combination (or “combo”) charts are a combination of column and line charts. They can be used to display changes in discrete values over time compared to a measurement like a mean, target, or expected value.
- Use when it is important to directly compare two different series that use the same measure (y-axis). A two-series column or horizontal bar chart can also be used, depending on the dataset.
- Because combo charts rely on line charts, the dataset should either be a time series or involve the ranking of items.
- Don’t use for data sets when the values along the x-axis are unrelated, because the line chart may imply a trend that does not exist.