A Global Comparative Analysis Of Urban Form Based On Urban Land Density Distribution

Urbanization with low density in spatial has been continuing to occur globally,which manifests the significance of revealing the types of urban forms and identifying the relevant influencing factors for urban planning.32 cities in the world,including mega-cities,large cities,and medium-sized cities,were selected.We extracted the impervious surface of the cities using the Landsat ETM+ images in 2010.Different partition methods(single center,balanced multi-centers and non-balanced multi-centers city)were employed on the basis of impervious surface density calculated in a series of 1km concentric rings.Each city was divided into the core area,inner urban area and suburban area based on an inverse S-shaped function of urban land density.The central versus decentralized dimension and compact versus sprawl dimension of urban form were defined.Thirty-two cities are divided into four classes by calculating the ratio of urban core area,inner urban area and suburb area to urban area.The urban centrality index and the urban compactness index are proposed based on different types of urban form.Further analysis of the impact of socio-economic development indicators including population density,economy,traffic,communication on city form were carried out.The majority of the cities are either decentralized-sprawl or central-compact,less of them are central-sprawl.Cities in developed and developing countries show different urban forms.The cities of developed countries are mainly manifested as "decentralized" and "sprawl".However,for the cities in developing countries,the proportion of urban form of decentralized-sprawl and central-compact is almost half.The correlation between urban form and city size is weak.Except population density,the socio-economic development indicators are found to be negatively correlated with the urban centrality index,but positively correlated with urban compactness index.(1)32 cities are eventually divided into three categories:the number of decentralized and sprawl cities is up to 18,the number of central and compact cities is 9,the number of central and sprawl cities is 5.The results of urban form classification show a law:the vast majority of urban form performance is either decentralized and sprawl type,either is central and compact states,less cities for the central and sprawl type.Urban form performances for the central while more performance for the compact;urban form performances for the decentralized type,then more performance for the sprawl type.(2)The type of the decentralized-sprawl cities are characterized by the rapid decline of the impervious surface density in the core area and the smaller range of the urban core area,the urban impervious surface density decreases slowly in the urban suburbs and the bigger range of low density area.The central-compact cities are characterized by that the city impervious surface density in the high density core area within the scope of the city core area decays slowly,the big proportion of urban core areas in the urban,urban impervious surface density decreases rapidly in the suburban area with the small proportion of low density area in urban.The central-sprawl cities characterized by the slow decline of the urban impervious surface density in the core area and the urban impervious surface density decline also slowly in the urban suburbs.(3)Analysis of urban form and urban social development level shows that urban forms in the developed level and the level of developing countries have a big difference.In the cities of developed countries,the urban form mainly manifested as decentralized,sprawl.However,cities in developing countries,the proportion of urban type decentralized-sprawl and central-compact is almost half.The relationship between urban form and the size of urban population is obtained that there almost no difference of urban form under different urban population size and the correlation between urban form and city size is weak.(4)Analysis of the correlation between social and economic development indicators and urban compactness index shows that except population density,the socio-economic development indicators found negatively correlated with the urban centrality index,but positively correlated with urban compactness index.