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School of the Built Environment
Faculty of Technology, Design and Environment
Over the last fifty years, research into street networks has gained prominence with a rapidly growing number of studies across disparate disciplines. These studies investigate a wide range of phenomena using a wealth of data and diverse analytical techniques. Starting within the fields of transport or infrastructure engineering, street networks have commonly been treated as sets of more or less homogeneous linear elements, connecting locations and intersecting at junctions. This view is commonly represented as a graph, which provides a common and rigorous formalisation accessible across disciplines and is particularly well-suited for problems such as flow optimisation and routing. Street networks are, however, complex objects of investigation and the way we model and then represent them as graphs has fundamental effects on the outcomes of a study. Many approaches to modelling street networks have been proposed, each lending itself to different analyses and supporting insights into diverse aspects of the urban system. Yet, this plurality and the relation between different models remains relatively obscure and unexplored. The motivations for adopting a given model of the network are also not always clear and often seem to follow disciplinary traditions. This paper provides an overview of key street network models and the prima facie merits of pertinent alternative approaches. It suggests greater attention to consistent use of terms and concepts, of graph representations and practical applications, and concludes with suggestions for possible ways forward.
A detailed critical analysis of the definitions of built form as used in urban morphology is reported. The overarching aim of the analysis was to establish a common reference point for examination of the different aspects of urban form in a given case and comparative study of cases from different times and places. Seminal works are examined in detail, in particular those of M. R. G. Conzen, Gianfranco Caniggia and Gian Luigi Maffei. The starting point is the common conception of a hierarchical relationship between buildings, plots and streets and the overlapping of aspects and elements. Different types of ambiguity inherent in the generic structure of built form are identified. Incorporation of these into a rigorous conception of the hierarchy that allows for the richness of overlapping sets reconciles earlier conceptions and accommodates a wide range of specific forms.