Urban expansion steady-state index of urban expansion based on remote sensing and GIS and its applications

Abstract: Urban expansion is a globalization trend nowadays, and how to measure the growing degree is a hotspot in the research of urban expansion. Road network is an extremely important factor that drives the increase of urban land. There is an interactive relationship between road network and urban land expansion. The research on the quantitative relationship between those 2 factors is helpful to provide an effective method for sustainable urban development. For the purpose of studying the quantitative index for steady-state urban expansion, in this paper, Beijing, New York, London and other 13 world-class cities were taken as the study areas, and the multi-period remote sensing images and vector data of urban road networks were adopted. Firstly, urban land use vector data were obtained through image interpretation with the aid of a remote sensing and GIS (geographic information system) platform. Then, overlay analysis was utilized to extract urban expansion information. A map of road network density was further generated and manufactured using the density analysis tool in ArcGIS. Secondly, the urban expansion - road network density model was established by regression analysis, which was used for fitting the relationship between road network density and urban expansion speed. Through the calculation and comparison of the sample cities' values of the turning point and thresholds for urban expansion, urban expansion steady-state index (UESI) was proposed, and then 13 sample cities' UESI values were calculated. Finally, the urban expansion state of Beijing in 2025 was predicted by using CA (cellular automaton) - Markov model and Logistic regression model. The results proved that (1) compared with the developed cities, Beijing's urban land expansion was in a serious situation in the past 30 years, and Beijing required the dispersal of population and function in the future; the road network density in Beijing was relatively low and presented a single center, which should be improved and optimized; (2) UESI could effectively quantify the trend of urban expansion; assuming that external environment of urban development was stable, the urban expansion was in a relatively steady state, while UESI reached 0.30. New York, London, Tokyo and other cities' UESIs were close to or greater than 0.30, while Beijing and Sao Paulo's UESIs were less than 0.20; Sydney's USEI was 0.21, which meant Sydney had a great potential for urban land expansion in the future; (3) according to urban expansion quantitative analysis and the theory of urban life cycle, the period of urban expansion could be divided into development period, growth period, maturity period and transition period; and the corresponding typical cities were Mexico City, Beijing, New York and Paris separately; (4) if the current city development trend was kept, the UESI of Beijing in 2025 would be 0.19, more than 0.17 in 2015, and the urban land expansion would remain in the growth period. UESI has the reference value for urban planning in fast-developing cities. The index effectively quantifies the status and potential of urban expansion, and enriches the quantitative study of urban expansion. Understanding the quantitative relationship between road network density and urban expansion is beneficial to define urban development phases, avoid the irregular expansion, and provide new ideas for addressing the inefficient utilization of land and other issues.