What does a pie/circle graph illustrate?

A pie or circle graph is specifically designed to illustrate the percentage of categories within a single topic, providing a visual representation of how each category contributes to the whole. Each segment of the pie represents a distinct category, and its size is proportional to the quantity or percentage of that category relative to the total. This format is especially effective for showing parts of a whole, making it easy for viewers to grasp the relative sizes and comparisons at a glance, thereby conveying information about proportions effectively.

Other types of graphs serve different purposes; for example, relationships between multiple variables are better illustrated with scatter plots, while comparisons of categories are typically shown using bar charts. Trends over a period of time are best represented by line graphs, where changes can be tracked and data can be evaluated over intervals. Thus, the pie graph's unique focus on relative percentages of a single topic distinguishes it from these other graph types.