Thus, the main new idea arising from catastrophe theory as discussed so far is that it is worthwhile being alert to the possibility of unusual types of system behaviour, and that the techniques of the theory can be used to formulate models to handle such behaviour. In the next section, we begin a preliminary treatment of some examples and follow this with a slightly more formal treatment of the basic concepts. 1.2 A preliminary outline of some examples 1.2.1 A remark on scale
As usual in urban and regional modelling, it is important to distinguish the different scales at which models are to be developed. The usual distinction of micro-, meso-and macroscales is useful here as elsewhere. At the micro scale, we are concerned with individual behaviour of some kind, and decisions, possibly under constraints (and with the resulting behaviour being in some cases determined more by the constraints than any notion of choice). At the meso scale, we deal with urban and regional spatial structure, and this is the scale which is at the heart of geographical analysis (even though it has to be intimately connected to other scales). At the macro scale, the city or region is characterised by a small number of aggregate variables.