ABSTRACT
Spatial interaction models simulate the journeys made between origins and destinations. The concept of maximum entropy has been applied to a generation of numerous interaction models such as residential location models, shopping models or the doubly constrained gravity model. The use of a gravity model within a framework of urban mobility was made by Casey, who applied this approach to simulate shopping trips made between the regional towns. Spatial interaction models have an aggregated nature because both space and the traveller characteristics can be grouped into large categories. So, instead of studying determined points in space, larger zones are defined containing many activities and occupations in which the number of journeys being produced and attracted is analysed. With the simply constrained models, the models constrained by the origin where only information about the origin of journey flows is available can be distinguished from the models constrained by destination where only information about the destinations of the journey flows is known.
