Legends summarize the distinguishing visual properties such as colors or texture used in the visualization. A legend or key helps the user build the necessary associations to make sense of the chart.
When possible, avoid using a legend and label data representations directly. Legends rely on visual association, which can make a chart more difficult to understand.
Your chart doesn’t need a legend if it only presents one data category. Only use a legend if you can’t safely assume there will be enough space to apply labels directly.
Use clear language and avoid acronyms in legends. This also applies to titles and axis labels.
Chart legends use color as the default distinguishing property for data sets and values. Texture can be used instead of, or in addition to, color to make your chart accessible for users with visual impairment.
The legends are positioned at the
top of a chart by default, under the chart’s title. Depending on the page’s layout and context, you may choose to position the legends at the
right of a chart with respect to the graph frame.
Position the legend at the top or bottom of a chart in situations where space is a scarce, such as a dashboard.
Position the legend to the right of the chart when space is plentiful, or when you would like to provide the maximum context.
Position the legend on the left of the chart when better type alignment is needed. Be sure the surrounding elements of the chart are not too closely clustered.
In geospatial charts, legends can be overlayed on top of a graph frame.
Hovering over the legend of one category lowers the opacity of all other categories in the chart to 30 percent.
Clicking on the legend of one category isolates the information, hiding all other categories. The legend gets a checkmark on click, switching to a selected state.
When all categories are selected, checkmarks in legends disappear and the legend resets to its default state.
Please note that hiding legends is discouraged in data visualizations unless only one category of data is displayed. This design is for mobile displays where offering legends at a glance is less essential. In general, hiding legends reduces the clarity of the visualization and is inaccessible.
Up to two lines of legends are displayed by default. Clicking on View more expands the legend area to show all legends. A legend should not be taller than 30 percent of the chart’s height.
When legends exceed 30 percent of the chart, overflow the content and scroll vertically.