It is a reductive graphic representation of the course or results of an action or process. Diagrams are enlisted at the formative moments of design to chart the potential relationship between concept and reality.

In functioning as a constructive doodle, and concerned more with idea than appearance, diagrams are graphic representations of an idea being structured.

However, the diagram is not the idea but a model of it; intended to define its characteristic features.

 According to the designer Keith Albarn, through appropriate structuring, diagrams may generate different notions or states of mind in the viewer. However, these ‘different notions or states of mind’ are susceptible to three factors that are also rooted in the designer’s mind: familiarity with the mode of expression, the amount of information that the drawing supplies and a previous experience of three-dimensional space.

 In order to develop an effective design model and to facilitate the evolution of forms in response to this model, a variety of diagrams, each with their own potential and conceptual set of rules that aid decision making, may be employed.

These include ‘schematic’ and ‘operational diagrams’ that are concerned with the relationship and orientation of the parts, and for visualizing changes over time. ‘Functional’, or ‘bubble diagrams’, identify the proximity and relative size of the zones of activity, while ‘flow diagrams’, like their operational counterparts, study possibilities that arise when movement is considered between one point and another.

  These are all analytical diagrams that investigate the nature of existing conditions and evaluate a completed design in comparison with its original intentions.