While complexity theory has become influential in the understanding, analysis and modelling of cities, it has been far less influential in planning and designing them. In complexity based analyses, cities are self-evidently complex adaptive systems, and this is a virtuous thing. A defining principle of complex adaptive systems is that they are scalar and hierarchical, i.e. global systems, such as cities, are formed by accumulations of other complex adaptive subsystems. This article argues that with the rise of the shopping centre and the decline of traditional precincts, the subsystems of the city, its regional, district and neighbourhood activity centres, have been increasingly organised by mechanical order rather than the self-organisation required of complexity. According to the principles of complexity theory, systems self-organised as complex adaptive systems will have greater mass and diversity, and be more resilient and stronger than systems organised via mechanical order. This article tested these principles by comparing activity centre mass and diversity between South Australian suburbs and towns. The research found that activity centres self-organised as complex adaptive systems do have greater mass and diversity than those organised via the mechanical order of the shopping centre.