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.
Color and texture
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
bottom of a chart by default. Depending on
the page’s layout and context, you may choose to position the legends at the
top, under the chart title,
right of a chart with respect to the
Bottom (default) and top
Position the legend at the bottom or top of a chart in situations where space is scarce, such as a dashboard.
Position the legend to the left of the chart when better type alignment is needed. Be sure the surrounding elements of the chart are not too closely clustered.
Position the legend to the right of the chart when space is plentiful, or when you would like to provide the maximum context. In mobile, the legend could revert to a stack.
Overlay (geospatial only)
In geospatial charts, legends can be overlayed on top of a graph frame as long as the legend has a background opacity of 80% of the chart’s background color. Since geospatial charts can vary drastically in appearance, the legend can be placed on either side of the chart, top- or bottom-aligned, whatever best accommodates the content.
To demonstrate the legend’s background opacity, we chose to place the legend at the top left in the chart below. See the Master data visualization design file for more detail about geospatial legends.
Hover to highlight
Hovering over the legend of one category lowers the opacity of all other categories in the chart to 30 percent.
Click to isolate
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.