It has been recognized that in [Sherman Act] § 2 cases identification of the relevant geographic market is a matter of analyzing competition. “The geographic market encompasses the area in which the defendant effectively competes with other … businesses for the distribution of the relevant product.” It is “defined in terms of where buyers can turn for alternative sources of supply.” The definition of the relevant geographic market, therefore, is a question of fact to be determined in the context of each case in acknowledgment of the commercial realties of the industry under consideration….

Ruggero J. Aldisert, Agatha D. Aldisert, Logic for Lawyers- A Guide …, loc. 1236