This research seeks to provide additional insight into the question of what travel markets should be included in a statewide model. Rather than focusing on travel model structures and formulations, this work instead focuses on an essential and often neglected part of any modeling exercise—understanding the nature of the system being modeled. Specifically, it involves identifying the major travel markets within a statewide model. The magnitude of each market is quantified through the use both of observed data and of model results and these markets are contrasted with what can be expected in an urban model. The results of this analysis provided a solid foundation to make informed judgments about both improvements needed within the model system, and data collection priorities. The context of this work is a case study for the state of Arizona, and it leverages the development of the Arizona Statewide Travel Demand Model: Phase 2 (AZTDM2). The work is of broad interest because many of the markets identified and development priorities can be expected to be common to many states, and because it provides a framework by which other states can analyze the travel markets most relevant to them.