2.1 Diagrams as models

Diagrams come in many forms and uses, but for systems thinking and practice it is useful to think of them as models (meaning ‘representations of reality’ in everyday usage). The term ‘model’ is used in a variety of contexts, even when there is a more commonly used term especially appropriate to its own context: models of terrain are usually called ‘maps’; models of electrical components wired together are usually called ‘circuit diagrams’; and models of the configuration of the planets within the zodiac are called ‘horoscopes’ (see Figure 1).

Figure 1 Examples of different diagrammatic models: (a) a street map, (b) a circuit diagram, and (c) a horoscope

However, systems practice usually goes beyond lay usage (i.e. models are ‘representations of reality’) to consider the representation of structures that do not readily exist, except in the mind. Thus a plan of a house not yet constructed or a diagram of the social relationships between a group of children can be usefully called a model. In each case we must be prepared to accept that there can be many different perceptions of this ‘reality’ by different people (different architects produce different plans). No perception can be singled out as being more ‘real’. Indeed, people may each have different internal models of ‘reality’, but may not appreciate that there can be such differences.

So to be useful, diagrams being used as external models need to follow agreed conventions and should select those features of most interest in a situation and show the relationships between them.

It is no accident that the three examples mentioned above concern relationships between the constituent elements:

1. the map deals with how each building is related to its neighbouring buildings;

2. the circuit diagram shows how each component is related (via wire connections) to other components;

3. the horoscope indicates the angular relationships of planets to each other and to the zodiacal signs.