Designing Charts: When to Include a Legend

Including a legend in your chart is essential to ensure your audience can accurately interpret the information in your data visualizations.

The following are some situations when you should include a legend in your chart: 

  • Multiple categories or data series: A legend is necessary if you have various categories or data series represented in your chart, for example, comparing annual sales of different products over several years. By including a legend, your audience can quickly identify which color or pattern corresponds to each product.
  • Different types of data points: If your chart contains different types of data points, such as markers for both actual values and projected or historical values, using a legend can assist viewers in understanding the context behind these data points.
  • Variation in colors, patterns, or symbols: If you use different colors, patterns, or symbols to represent various aspects of your data, including a legend, it assists viewers in making sense of the visual distinctions.
  • Complex or multi-dimensional data: When presenting complex or multi-dimensional data, a legend can provide the necessary guidance for viewers to understand the structure of the data.

You should include a legend in your chart whenever it helps your audience understand the data better by clarifying categories, data series, or types of data points and when representing complex or multi-dimensional data.