THE THEORY OF THE NATURAL URBAN TRANSFORMATION PROCESS: THE RELATIONSHIP BETWEEN STREET NETWORK CONFIGURATION, DENSITY AND DEGREE OF FUNCTION MIXTURE OF BUILT ENVIRONMENTS Akkelies van Nes 1, Yu Ye 2 1 Department of Urbanism, Faculty of Architecture, Delft University of Technology, P. O. Box 5043, 2600 CR Delft, the Netherlands, Email: A.vanNes@tudelft.nl 2 Department of Urban Planning & Design, The University of Hong Kong; 8/F, Knowles Building, Pokfulam Road, Hong Kong, Email: yuye@connect.hku.hk Key words: space syntax, building density, land use, urban morphology, urban design During the last decade, advances in software, spatial analyses methods, and improved capacity of computers have made it possible to quantitatively analyse morphological features of whole cities. This emerging trend of combining geographic information system (GIS) with traditional urban morphology brings some new insights into the evolving logic of urban form and related functions. In this respect, this paper aims to propose a draft of a theory on the natural urban transformation process. This theory accounts for built environments that are not affected by rigid planning systems, regulation plans, various trusts connected to plots, religious aspects, collective memories, historic artefacts and urban areas protected by law. This theory is supported by quantitatively analysis of various morphological elements in a series of Dutch towns through the use of Geographical information systems (GIS). 1. THE OUTLINE OF THE THEORY OF THE NATURAL URBAN TRANSFORMATION PROCESS In the era of big data analysis, it is possible to gather and to analyse a large amount of spatial and socio-economic data on a metropolitan scale level. However, there is a need to develop and to update theories on how cities functions spatially and socio-economically useful for urban design and planning practice based on these empirical findings. For instance, research with the use of the space syntax has contributed to a theory of the natural movement economic process (Hillier et al., 1993), which claims that the spatial configuration of the street network configuration influences the flow of movement and location of economic activities. The results from our inquiry suggest a first draft of a theory of the natural urban transformation processes. An urban transformation process is a process when an urban area transform from a deserted to a vital and attractive place. Urban transformation is spatially dependent on the street network configuration containing streets with high spatial integration
values on various scales aggregating high building density and a high degree of land use diversity. The spatial configuration of the street network, as the foundation, influences the degree of density and functional mix. Likewise, the degree of density influences the degree of functional mix. This theory contrasts with current planning practice in America, several European as well as Asian countries. The road and street structure is mostly decided by the road engineer, influenced by the various street and road manuals based on the Buchanan report from the 1960 s. The focus of these reports is to enhance traffic safety and smooth traffic flow on the cost of vibrant urban street life. Furthermore, the focus is mostly on making a mobility network with purpose to serve urban functions (van Nes, 2002). Therefore, current urban design and planning practice is heavily influenced by street and road standards and structures provided by the various manuals from the public road authorities. As research has shown, land use development and building densities adjust themselves accordingly to the degree of street network integration in built environments in a natural urban transformation process. If an urban area has low spatial integration on its street and road network or is poorly connected to its surroundings, the area tend to be mono-functional, have imbalances on the FSI and GSI of the build mass, and lack street life and a diverse economic activities. Conversely, an urban area with high spatial integration on its street and road network tends to be multi-functional with high density of the build mass and have a vibrant street life (Ye and van Nes, 2013; van Nes et al., 2012). Therefore, the spatial structure of the street and road networks matter in how urban areas transform through time. 2. EMPIRICAL SUPPORT Various analyses tools have been developed for analysing morphological elements, like the mixed-use index (MXI) method (van den Hoek, 2009) and the spacematrix method (Berghauser-Pont and Haupt, 2010) for quantifying the degree of land-use diversity and density of built-mass respectively. Moreover, the space syntax method (Hillier et al., 1993) is able to calculate the degree of spatial integration and degree of inter-connectivity of the street network on various scale levels. Van Nes et al. (2012) initially attempted the way of converting space syntax, spacematrix, and MXI analyses separately into a GIS framework. The strong correlations between street network integration and density in the Rotterdam case prompted the authors to seek a better analytical method combining all the three analytical tools to represent to certain extent the entire urban form. Through Ye and van Nes a set of explorations (2013, 2014), a quantitative classification system on various types of urban areas can be presented. These types of urban areas are ranked from suburban areas to low urban areas, in-between urban areas, middle urban areas and finally highly urban areas. The ranking of these types of urban areas are based on the
values from the quantitative analyses on degree of land use diversity, building densities and street network integration. This morphological classification is able to indicate an urban area s degree of socio-economic performance, in other words, various degrees of urbanity. Normally, a highly integrated area with high building density and high degree of functional mixture should be more urban than a mono-functional urban area with low street network integration and low building densities. The theory of natural urban transformation process is inspired from a common sense that road exists in average for thousand years, a building typically stands for about 100 years, and the functions inside tend to change frequently (van Nes, 2002). This assumption is verified by selecting a set of new and old towns with similar sizes and regional positions but belongs to different urban transformation phases from newly build to well-settled. The application of our quantitative analytical method on these cases showed how street network integration, building density and typology, and degree of land-use mixture are inter-acting with one another in different phases of an urban transformation process. Four towns in the Netherlands (Lelystad, Alemere, Zoetermeer and Haarlem) are chosen for testing. A set of available socio-economic indicators, including population density, employment opportunities, population diversity, facilities, and percentage of creative class, etc., are used to judge the various phases of the urban transformation of these towns. From the socioeconomic indicators, these towns can be ranked as follows: Haarlem scores highest, followed by Zoetermeer, Almere, and Lelystad. The degree of urbanity from a morphological perspective in the four Dutch towns was quantified with our proposed method. The results are in line with the socio-economic ranking. Lelystad the new town ranking lowest in both perspectives has the highest percentage of suburban areas. Conversely, Haarlem has the highest number of highly urban areas and the lowest number of sub-urban areas. Detailed observations are made from the four cases to respond the assumption of interacted relationships between various spatial elements. Lelystad performs most poorly in terms of density and functional mix. Almere has relatively higher built-mass density than Lelystad, but lacks land-use diversity. Zoetermeer and Haarlem have high degrees of land-use diversity in their centres. As the results show, the degrees of building density and land use mixture increase over time in a natural urban transformation process. Spatial integration of street networks tends to remain stable for a longer time period than building density and land use. Therefore, a natural urban transformation process is spatially based on the accumulation of building density and land use diversity supported by a well-integrated street networks. A further verification is made to investigate the relationship between the percentages of high and middle integrated street networks from the space syntax analysis with other high and
medium values from the other two spatial variables. The results of dividing high and middle integrated values from the space syntax analysis by all high and middle valued values from all three spatial measurements gives the following results: 6.8 % in Lelystad, 8.4% in Almere, 18.3% in Zoetermeer, and to 36.8% in Haarlem. This calculation supports that the degree of street network integration steer urban transformation processes. 3. CONCLUSIONS This paper presents an attempt to provide a theory on built environments transformation processes useful for spatial planning and urban design. This theory is based on quantitative empirical support for processes of morphogenesis and inherent relationships between various spatial components. Nevertheless, more cases are needed to validate and to fine-tune this draft of the theory of the natural urban transformation process. So far, the proposed theory states that there are interrelationships between street network configuration, building density and land use. Therefore, this theory can be applied in improving the spatial components in current new town developments for preventing dull, mono-functional, deserted modern town centres with a lack of street life and micro scale businesses. At present several European new towns needs revitalisation, but lacks knowledge on the spatial parameters. Moreover, large-scale Asian new towns are implemented in a short time span. Pursuing good place-making can be guided by this theory. Seemingly, providing a well-integrated street network on various scale levels steers the further transformation processes of the degree of building density and land use diversity. The street network configuration is the spatial armature for generating the socio-economic life in cities, and not visa versa. REFERENCES: Berghauser-Pont, M. and Haupt, P. 2010. Spacematrix: Space, Density and Urban Form, NAI, Amsterdam. Hillier, B., Penn, A., Hanson, J., Grajewski, T. and Xu, J. 1993. Natural Movement: or configuration and attraction in urban pedestrian movement. Environment and Planning B, 20(1), pp. 29-66. van den Hoek, J. 2009. The Mixed Use Index (Mixed-use Index) as Planning Tool for (New) Towns in the 21st Century. In: Stolk, E. and Brömmelstroet, M. T. (eds.) New Towns for the 21st Century: the Planned vs, the Unplanned city. Amsterdam, NL: SUN Architecture. van Nes, A. 2002. Road building and urban change. The effect of ring roads on the dispersal of shop and retail in Western European towns and cities. PhD thesis. Agricultural University of Norway. van Nes, A., Berghauser-Pont, M. and Mashhoodi, B. 2012. Combination of Space Syntax with
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