Modeling Interregional Interaction: Implications for Defining Functional Regions

The concept of the functional region is intimately linked to selectivity in human interaction and the ratio of within-region to between-region interaction has often been cited as a possible basis for delimiting functional regions. This paper extends the well-known spatial interaction model to the analysis of interregional and intraregional interactions. The Interregional Interaction Model explains the behavioral phenomena that we recognize as functional distance and functional regions, and calibration of the model amounts to their objective delimitation. Regionally biased interactions are simulated, and the embedded regional structure successfully recovered in a series of tests, even when substantial error components are introduced into the simulations. A heuristic calibration technique is developed for large problems. The heuristic is used to partition the United States into two functional regions, based on student migration matrices. A cluster of southeastern states consistently emerges as a functional region distinct from the north.