Spatial competit ion and agglomeration in urban modelling

Many forms of urban models are retail oriented, that is, they depend to some degree on the allocation of shopping expenditures to particular destinations. Such an allocation is usually undertaken with the aid of a production-constrained gravity model, although this type of model ignores the relationship between retail expenditure patterns and spatial competition and agglomeration forces. The effect of such a relationship on urban structure is examined with the aid of a production-constrained competing destinations model in three situations: (1) in a simple facility -location problem, (2) in a Garin-Lowry model, and (3) in the use of catastrophe theory and bifurcation theory to examine urban dynamics. The replacement of the gravity model by the competing destinations model is shown to produce more realistic urban models and leads to new insights into structural dynamics.