What is the primary purpose of using a legend on a graph?

The primary purpose of using a legend on a graph is to indicate different data series represented. A legend serves as a key that helps viewers understand what each visual element of the graph—such as colors, patterns, or symbols—corresponds to in terms of the data being presented. This is particularly important in graphs that contain multiple datasets, as it allows the audience to easily differentiate between them and comprehend the relationships or comparisons being illustrated.

In contrast, while listing data sources is important for transparency and credibility, it is not the main function of the legend. Similarly, providing a title for the graph is essential for setting the context, but this is not the role of the legend. Outlining the methodology used is critical for understanding how the data was collected and analyzed, but again, it does not pertain to the function of a legend. Hence, the correct answer emphasizes the role of the legend in clarifying the various data series presented in the graph.