The Micro-economic models described in the previous chapter can be defined as belonging to a disaggregated approach, because the analysis centres around the behaviour of individual units. The approach taken by spatial interaction models, by contrast, can be defined as aggregate, because both space and activities are grouped into discrete categories. Instead of analysing particular points in space, zones containing a large number of activities are defined. Activities, on the other hand, are aggregated into groups, and it is assumed that all the individual members of a group have similar characteristics.

Origins and development of spatial interaction models

There is a considerable amount of literature on spatial interaction models, so that only a brief review is presented in this section. Excellent reviews are contained in Lee (1973), Batty (1975, 1976), and Baxter (1976). In spite of earlier work by Reilly (1931), Hoyt (1939), Stewart (1948), Zipf (1949), Converse (1949), Clark (1951), Isard (1956), and others, most authors agree on placing the origins of modern spatial interaction models in 1959 with the work of Hansen. After this, a flurry of research activity took place.

There are many factors which led to the rapid growth of this area of research, but perhaps the most important one is that spatial interaction models are easy to apply to real cases, producing useful and realistic results. Another factor is that the spatial interaction approach is particularly relevant to transportation analysis.