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  • According to the urban scale grade in China


    According to the urban scale grade in China, a large city is one with a buy EZ Cap Reagent GG (3\' OMe) between 1 million and 5 million, and a megacity has a city population that exceeds 10 million. Nanjing, the capital city of Jiangsu province and the political, economic, and cultural center of the province, has a population of approximately 10 million. It is also one of the most important cities among the large cities of Southeast China (Figure 2). The characteristics of urban growth in large cities of Southeast China focus on the high speed of urban growth and its measure to control urban growth to achieve the goal of sustainable development. We believe that the urban growth process in Nanjing represents the characteristics of large cities in Southeast China. Thus, we simulate the urban growth of Nanjing in our case study.
    Findings and discussion
    Acknowledgments The author gratefully acknowledges the assistance of Xu Mingyao, director of the urban planning bureau of Nanjing, who provided relative historical maps and information on the city. This study is supported by the National Natural Science Young Foundation of China (No. 51308101) and the National Natural Science Foundation of China (No. 51378101).
    Introduction Hierarchy is an essential phenomenon in transport networks. Immers et al. (2004) stated that hierarchical transport networks result from the interaction between the demand and supply of the transport system. In the long run, the highly intensive usage of some routes can lead to improved facilities and investments, while the less used routes become neglected. In this way, the hierarchy of the network is continuously strengthened. Immers et al. argued that the railway networks developed in the early 19th century accelerated the hierarchical development of transport networks and spatial structures. Wang et al. (2012) suggested that each transport mode has its own network hierarchies, which depend on the territorial scales and other natural and social factors in a particular country. Hierarchical transport networks are embedded in the hierarchy of urban networks. Several scholars have investigated the close interrelationships between these two systems. The pioneering study of Haggett et al. (1977) revealed that transport network development is an evolutionary process resulting from the substitution of routes among successively higher-order centers and the emergence of an urban hierarchy. Van Nes (2002) showed that the hierarchy in transport network levels is closely linked to that in settlements, and that each transport network level connects cities of a specific rank to higher-ranking cities. Immers et al. (2004) suggested that when planning an ideal transport network, one should first define how many and which cities should be incorporated in such network and in what order of importance. Although the abovementioned studies provide clear insights about the hierarchy phenomenon, transport networks must be investigated along with the existing hierarchical structure of urban systems to understand the logical structure of transport systems. Regarded as the “transport modes of the future” (UIC, 2010), high-speed rail (HSR) networks are rapidly expanding in many countries. A long-term national HSR network was enthusiastically planned and implemented in China over the past decade. From 2004 to 2014, more than 11,000km of new HSR routes were utilized for service. By 2020, the Chinese HSR network is expected to reach approximately 18,000km, which accounts for more than half of the overall length of HSRs worldwide (Zhang and Nie, 2010). However, compared with such an unprecedented HSR network expansion, the hierarchical structure of China׳s HSR network planning remains a “black box” (Graham and Marvin, 2003). Only few studies have investigated the interrelatedness between Chinese HSR network planning and urban hierarchies, especially at the national level (e.g., Wang and Long, 2009; Wang and Jiao, 2014). The majority of existing research focuses on how HSR improves the accessibility of hub cities or changes the spatiotemporal structure of urban agglomerations. In other words, HSR is only of peripheral interest and serves as a tool to analyze the urban system.