PRIOR STRUCTURE AND SPATIAL INTERACTION

A rationale for continued interest in simple, static urban models, such as the gravity-type models, is given through the perspective of the notion of prior structure, according to which there is, embedded in every model, a largely non-empirical component resulting from the structural properties of the theoretical language used. It is suggested that the prior structure implicit in gravity models is responsible for the widely observed map effect in spatial interaction as well as for the relative predictive power of these models. A procedure is outlined for deriving that prior structure from first principles. Combined with a minimal amount of behavioural information, that quasi-analytic component can be used as prior information, in the Bayesian sense, to generate familiar forms of the gravity model as the most probable consequences of svstem specification. The practical significance of the prior-structure effect for model performance is then briefly discussed.