ABSTRACT
Development of typologies of systems application has resulted in long lists of different types of systems based on a range of criteria. Chorley and Kennedy (1971) provide one of the first based on the form and function and complexity of the systems studied. Complexity increases from simple cascading and morphological systems to processresponse systems and on to biological and social systems. Strahler (1980) develops a typology based on similar criteria to Chorley and Kennedy. Terjung (1976) uses four criteria to separate system modelling in physical geography into different levels. The criteria used relate to the type of logical argument used in explanation (induction or deduction), the level of explanation (individual entities or the system as a whole), the degree of deterministic behaviour and finally the level of description as opposed to explanation. An important basis for these typologies is the increasing openness of the systems. Isolated systems are an ideal type, ones where there is no movement of matter or energy across system boundaries. Closed systems permit the flow of energy across boundaries, but not matter. Open systems permit the flow of both energy and matter across their boundaries. These distinctions are important as they begin to define the expected behaviour of systems. The definitions derive from physics, where an isolated system will tend towards an equalization of the distribution of energy within it and hence eventually exhibit maximum entropy and disorder or randomness in the organization of its components. Systems that have their boundaries open to flows – particularly if these are of both energy and matter – are able to stave off this ‘entropy death’ as they retain their organizational structure. Open systems are viewed as able to retain both entities and relationships by maintaining gradients of energy levels between different system components. Flows from high to low energy are maintained and so the entities and relationships, the network that produces the system, are maintained. Energy and matter are derived from beyond the boundaries of the system to maintain that system. Although the overall entropy within the universe may be heading towards a maximum level, the smaller system being studied is able to reverse this trend within it by importing energy and matter to maintain its order. Entropy is kept at bay by continually exporting disorder and ‘borrowing’ energy to keep order.
