What are some common uses for vertical line graphs?

One common mathematical use for graphs of vertical lines is to determine whether or not another graph qualifies as a function. Vertical line graphs also have applications in the world of marketing and finance, such as plotting the amount of a product sold when its price remains static.

When the x axis of a graph is defined as the price of a particular product being sold and the y axis of the same graph is defined as the total amount of the product that has been sold, the resulting graph will be a vertical line if the price of the product does not change. The Vertical Line Test is an application of vertical line graphs that allows mathematicians to determine if a particular graph is a function or not; if the graph passes through any possible vertical line more than once, it is not a function.