Distance Deterrence Effects in Constrained Spatial Interaction Models of Interprovincial Migration*

Distance has long been viewed as a barrier to population migration, and there are numerous studies that identify the existence of a "dis­ tance decay effect" in migration and in other types of spatial interac­ tion [5;8]. Traditionally the relationship between distance and migra­ tion has been examined with the use of the well-known gravity mode!, which is based on an analogy with Newtonian mechanics. Wilson, however, [32;33] was among the first to show that gravity-type inter­ action models can be derived, alternatively, from either statistical mechanics or information theoretic methods, utilizing the concept of entropy maximization. In general, the method of entropy maximiza­ tion allows unbiased estimates to be made of the form of probability distributions, given limited prior information [18;21;30]. These esti ­ mates can then be employed in mathematical models of the system of interest that are to be tested against the observed data. In addition, the introduction of information in the form of constraints allows greater model flexibility and also overcomes the internaI consistency problem inherent in the classical gravity model [13;20]. As is the case with classical gravity models, information theoretic entropy maximizing models emphasize the role of the distance variable