Two interpretations of complexity are often considered in beginning thedesign and documentation for a project, namelyDesign complexity is by far the more popular indicator of manual drafting task magnitude, because it is visible before work commences. Appearances, however, can be misleading. In CAD production, magnitude of a task is highly dependent upon interpretation. What the designer chooses to model and the chosen methods of representation may not be known at the beginning of a design project. Superficial aspects of drawings and photographic images can mislead and short circuit a designer's detailed analysis and planning at the commencement of their CAD task unless they are balanced by equally clear notions of the intended model.

CAD complexity is associated with the actual CAD embodiment of the design.It derives from the strategic use of CAD functions applied to both organisationand production of the completed model. It is potentially a more usefulnotion than design complexity, because it directly concerns task outcomes,but it appears to have been underutilised. There are several reasons whythis may be so.

First, the concept of complexity is not entirely clear (Corning, 1998). CAD complexity is even less clear, being easier to describe in the negative, by defining what it isn't rather than what it is. Although there is an abundance of published literature on complexity in general, it is mostly in the areas of computer science, information theory, thermodynamics and biological sciences (e.g., Garey, Johnson, 1979; Shannon, Weaver, 1963; Simon, 1996), with relatively little directly relevant to CAD. There is a need to clarify the sense of the term "CAD complexity".

A second reason is that CAD complexity is not evident from the appearance of CAD drawings generated from a completed model. Possible indicators of complexity, such as the number of files or file sizes, are no more revealing unless some account is taken of the file contents. There is a need to identify the essential components of CAD complexity.

Informal observations of students in the Faculty of Architecture at the University of Sydney indicate that many find it difficult to appreciate the deeper organisational aspects of CAD until their work is well advanced. A likely reason for this is the need for less experienced CAD users to see the consequences of different strategies in order to understand their significance. At a later stage in the course of a project, the possession of a tangible model to see and discuss is evidently helpful as well.

We propose that development of a coherent nomenclature of CAD complexity will help to improve understanding of the task, particularly before modelling commences. We also believe that deeper understanding of CAD complexity may be useful in design management as well as education, and could assist design documentation in various disciplines.

This greater understanding may have a positive impact on both education and practice, by:

Other more strategic uses of CAD complexity concepts may include supportfor the development of: