Venn diagrams consist of circles that overlap other circles to a degree that indicates the two circles’ shared aspect. A circle that represents female lawyers in US corporations, for instance, would overlap perhaps 35 percent of a circle that represents all lawyers in corporations. In a three-circle Venn diagram, more relationships can be represented.
For example, a law department could show for its four primary corporate firms how large a slice of the litigation pie they handle. Visualize four circles, and have those circles overlap another circle that represents the total amount paid for litigation representation. The amount of the overlap of each circle would correspond to the corporate firm’s proportion of litigation work.
Another step is to make the size of each circle correspond to an amount, such as the total amount spent on the firm in the past year. Then the Venn diagram conveys both absolute dollars and percentage of the litigation spend pie. If you color the Venn circles, you can depict even more information.
The visual imagery of Venn diagrams helps for some people understand the relative size and interaction of quantifiable concepts.