Transportation Geography and Network Science/Morphology

Morphology, in the context of transportation geography, is better known as urban morphology which emerged as a topic resulting from the combined works of geography, architecture, sociology and urban planning. It studies the evolution and current transformations of urban forms, as well as the understanding its components (which include buildings, streets and parks to name a few) and their interactions. These interactions include both between the individual components as well as between the components and the urban form itself. Examples of urban forms range from cities, towns and villages though is not limited to this list as urban forms are defined as areas settled by humans. Since urban morphology involves the extensive study of spatial patterns of land-use, it serves useful for: urban design and planning as well as many traffic and transportation models which depend on land-use.

Perspectives

Historically, urban morphology existed as a topic fragmented between different disciplines before it evolved into an interdisciplinary field of study through platforms such as on the 'International Seminar on Urban Form'. Urban morphology was developed from the British Morphological School, the Italian Typological School and the French Versailles School from where the different disciplines of geography, architecture and sociology respectively were able to provide a perspective on a subject related to all of them. Hence, in urban morphology the development of the urban form is approached through the analysis of social and economic forces affecting them. Other approaches have included understanding (the urban form of) cities within the discipline of the spatial sciences through the construction of spatial dynamics models.

Geography

From the British Morphological School, geographer M.R.G Conzen is associated with developing the plan analysis which uses historical maps to understand the evolution of a town or city. Conzen introduced the method with a case study of the English town Alnwick. Implications of the method provide insight into land-use patterns and building forms. Considering a town plan as being comprised of its elements - a street network, plots and buildings - Plan Analysis uses unique combinations of these elements, called plan-units, to divide a town into regions of homogeneous morphology . This and other similar case studies for other European cities and towns provided the foundation for much of the conceptual framework for urban morphology. Expanding upon the urban morphological element of streets, from a geographic perspective the discussion on streets is important to identify street patterns in urban areas with the development of the classification system (or typology) of streets by type. For a towns and cities, degrees of regularities between different street layouts have been used as a means of classification. Other means of classification include deciding the configuration of the street layout - for example grid, axial plan and radial plan - for a town or city to visual spatial patterns. However, this classification method draws criticism for its simplistic reduction (sometimes misleading) of the complexity of the morphology of street patterns; urban street patterns tend to be composite. Urban street layouts embed the social and economic (also in some cases political) causes that have developed them in the past. Thus, looking at street layouts from a sole design point of view misses the understanding of how it has been shaped and renders it difficult to view its morphological characteristics. This, in part, is what motivates and highlights the usefulness of using Conzenian concepts of plan-units.

Architecture and Sociology

During the transformation stage of any urban landscape, the role of the agents who are in the position of influencing the physical shape of the urban form must be considered. Other than the developers and urban planners, architects play a significant role as having their ideas realized on the scale of the urban form, as well as be involved in the design and configuration of parts of urban areas. This is evidenced in the history of the urban morphology, with the development of the map by Giambattista Nolli for Rome which leads to the formalisation of the 'figure-ground theory': representing urban areas with solid masses and open voids. Another important architectural theory is the 'linkage theory' which aims to construct a 'network of lines' connecting the elements of an urban area. In this context, this refers to the arrangement of streets, pedestrian ways and other linear open spaces. Since the urban form is developed by humans one may expect that the urban form reflects a particular set of historical, social and cultural values. This forms the basis of the one of the main architectural theories, 'Place Theory', which imprints the contemporary societal values to physical environment,. Through the reflection of societal values one is lead to the idea of how the urban form design can be (and has) illustrate an aesthetic reflecting on ideas from religion (such as in the case of ‘the inward city ‘ and ‘nested city’). Within the architectural discipline, it should be mentioned that designs for the urban form have centred around a transport system. Examples of which include: the Star where a large city has a highly dense and used centre with transit lines radiating (from the centre); and the Linear City where the city (with its economic activities and residencies) is distributed along continuous transport line .

Spatial Analytics

Bottom-up Growth of cells in a neighbourhood deterministically in (a) and stochastically in (b) using the model of Cellular Automaton.

Understanding the evolution of the urban form also involves analytical methods - Geographic Information System (GIS), Cellular Automaton and agent-based models - by considering the urban form as a spatial structure. These perspectives leads creates new avenues of approaching evolution of urban form by involving the phenomenon of fractals into the conceptual framework for urban forms. The urban form is studied through different scales to better analyse the activity distribution which impacts the urban form. Many static equilibrium models are able to model the urban form since the urban structure with employment and population distribution is inputted into the model which illustrates morphological characteristics. The dynamic models based on cellular automata are able to generate processes (in the urban form) which illustrate features of agglomeration and bottom-up development from simulated urban areas. Results generated from simulated growths of cities from single seeds exhibit fractal patterns similar to real cities. However, there is a hidden assumption of the spatial patterns scaling through time that does not capture phenomena of radical societal changes such as in technology. This highlights a limitation within cellular automaton that could be addressed in the future. Another application of the tools within spatial analytics enables the urban form to be modelled as networks of human settlement encompassing a space where people are (in)directly connected to each other. A result of the application was a relationship between the levels of self-organisation (within cities) and the degree of network connectivity (relative to the network's spatial density). A unique feature of this relationship exhibited is how there is a minimum degree of network connectivity required to generate a level of self-organisation sufficiently large for the urban form to function as a metropolis. Increasing network connectivity achieves the functioning of a metropolis but renders the network redundant and inefficient, while decreasing the network connectivity does not achieve the performance of a metropolis.

Influence on Transportation

The evolution of the urban form (distribution of the employment and population in the urban area) is affected by processes of urban development through economic agglomeration. The overall effect on land-use within urban areas impacts how transport systems are used. Examples of which can be seen in the studies of patterns of metropolitan forms in the US where cities have low development densities and decentralised land-uses, thus encouraging the use of cars. While the opposite (high development density and centralised land-use), which is more prevalent in Europe, encourages the modes of walking and bicycle. These examples also allude to the idea of how effective designs of urban forms can address traffic problems. Hence, suggestions have been made for traffic policies to be based on population characteristics and spatial structure of cities at different stages.

The 4 main types of Urban Spatial Structures constructed with Transport Systems

Within metropolitan areas there are 4 main types of spatial network structures to consider:

• Completely Motorised Network: a large automobile-oriented network (with a land-use density ranging between low and average) of high-capacity highways while the public transit system is present with a minor function within the network. The network is to symbolise urban efficiency and designed to allow ease of movement between any 2 locations. E.g. North American Cities of Los Angeles and Dallas after 1950.
• Weak Centre: a moderately dense (in terms of land-use) network of concentric patterns where many centres along the periphery connected by ring roads compete with the central business district for economic activity. At the centre of the network is where the central business district is located, better accessed by car but connected by a transit service which is under-used and underfunded. E.g. cities such as Melbourne and San Francisco at the beginning of the 20^th century.
• Strong Centre: A highly dense network which is highly accessible by a high-capacity transit system responsible for serving the mobility requirements to generate the economic productivity in the central urban area. The radial and ring roads as well as high costs associated to the central business district motivates secondary centres to emerge away from the district along the ring roads. E.g. cities with high commercial and financial centres especially in the 19^th century such as in Paris.
• Traffic Limitation: Networks where traffic control and modal preference strategies are implemented. Its central urban area, served by a transit system, limits car use within it as part of a congestion management policy. The 'funnel effect' is illustrated through the use of individual transportation (car) relative to one's distance to the central area: decreasing as one moves towards central area while increasing as one moves towards the periphery. While the opposite illustrated by collective transportation (transit) use: increasing as one moves towards the central urban area but decreasing as one moves towards the periphery. Additionally, interfaces are present within the transportation system between suburbs and central area allowing access between individual and collective transportation modes (car and transit), and between high and low capacity collective transportation modes (bus and rail). E.g. Cities with such spatial structures may include Singapore and Hong Kong.

A significant process that has shaped transportation system within the urban landscape has been urbanisation - population shifts from rural to urban areas. Features of which have been imprinted onto the urban form through the concentration of activities on different scales: when it occurs relative to the entire urban area it is centralisation; but a focus within a part of an urban area refers to clustering. The urban spatial structure can be abstracted with network elements of nodes representing centre of economic activities (transportation facilities of train stations and airports) and linkages between the centres. It should be noted that nodes and linkages also illustrate the accessibility and mobility (of the urban transport system) which contribute to the evolution of the urban form. Limitations in the transport technology, historically, manifest much of the motivations for centralisation of activities at urban central areas due to the unavailability of cars and restricting people within urban areas to rely on walking as the main transportation mode. Due to the inefficiency of walking (as a mode) in achieving urban mobility, in the past many spatial structures of cities were highly compact and accessible; many cities in Europe and East Asia still retain similar structures. Additionally, the evolution of the urban form points to the influence transport technologies have on the urban form. A phenomenon exemplifying this are the new clusters that emerged in the periphery of urban areas, preempting the poly-centric form many urban areas have adopted with high car use.

Further Reading

• ISUF
• Fractal dimension on networks
• Cellular automaton
• Urban Form and Function