Which of the following best describes a use case for Reference lines in visualizations?

A use case for reference lines in visualizations is effectively captured by highlighting a target performance level in a chart. Reference lines serve as visual aids that help users quickly identify specific values, such as goals, averages, or thresholds, within a dataset. By incorporating a reference line, viewers can assess how data points relate to the reference level, making it easier to evaluate performance against set expectations or targets.

Using reference lines enhances the interpretability of the visualization, providing context that guides decision-making. For instance, in a sales performance chart, a reference line might represent a sales target, allowing users to instantly see whether actual sales are below, at, or above this target, which can be crucial for assessing business performance.

The other options do not effectively illustrate the primary purpose of reference lines. Comparing two different datasets over time typically relies on lines, bars, or other markers representing each dataset, rather than a single reference line. Changing the color of graph elements relates more to aesthetic modifications rather than performance benchmarks. Lastly, pie charts are used to represent proportional data rather than incorporating reference levels.