2.1 Introduction
One of the difficulties we face in trying to analyse the integrated regional systems described in Chapter 1 is that there is no obvious or single point of entry. Indeed, the more integrated the system, the harder it is to crack. Thus in the case of nodal regions, it is just as logical to begin with the study of settlements as with the study of routes. As Isard comments: the maze of interdependencies in reality is indeed formidable, its tale unending, its circularity unquestionable. Yet its dissection is imperative ... at some point we must cut into its circumference' (Isard et at, 1960, p. 3). We choose to make that cut with spatial interactions or movements. This chapter outlines the various types of movement that are important in the build-up of other parts of the regional system and reviews some of the models that have been evolved to describe their pattern. The idea of interaction leads on to a consideration of the natural fields that are created by them and to the difficulties that arise when overlapping fields need to be demarcated. Ideas of spatial diffusion—movement through time—are treated as a separate theme in Chapter 7.