Comprehensive Delimitation and Ring Identification on Urban Spatial Radiation of Regional Central Cities: Case Study of Zhengzhou

In China and a number of other countries, recent years have seen a prevailing trend in collective and cooperative urban development, transforming individual cities to polycentric metropolis. Such a phenomenon, also termed urban agglomeration by some researchers in China, has gradually become the main body of urbanization and the basic terrain unit in participating international competition and international division of labor. However, the spatial delimitation of urban agglomeration has been historically heavily influenced by subjective administrative instruction, as opposed to being primarily driven by radiation effects by regional central cities. To better delimitate the urban agglomeration sphere in China and other fast-developing areas, this work seeks to scientifically assess and comprehensively delimitate the spatial patterns of regional central cities’ radiation through quantitative analysis and modeling. Zhengzhou, a typical regional central city in central China is chosen as the study case. First, it makes a modification to the traditional gravity model by constructing a radiation quality index (RQI) and integrating distances representing commuter traffic, economic development gap, and cultural psychological factors. Subsequently, a comprehensive delimitation is derived that demarcates and describes Zhengzhou’s urban radiation toward 42 neighboring cities by applying the radiation field intensity model, radiation effect function, and judgment vectors of the urban radiation ring-layer model. The chief findings are that Zhengzhou’s radiation effect is not prominent compared to other similar provincial capital-level cities. There is no distinct psychological or spatial differentiation between Zhengzhou and its 42 neighboring cities. The economic distance between Zhengzhou and other cities has been stable, and has even shrunk, whereas there are notable differences among fixed range ring patterns. The interaction forces between Zhengzhou and neighboring cities have increased, and radiation field intensity of Zhengzhou has been expanded to outer rings. However, some cities along the provincial boundary received very limited influence from Zhengzhou, and are significantly more influenced by other radiation sources. In 2001 and 2009, there were 26 and 24 cities that fell in Zhengzhou’s urban radiation rings, respectively, whereas only seven cities were included in the core and primary radiation ring. This list of seven cities excluded Luohe City, in spite of its administrative inclusion within Zhengzhou. Zhengzhou’s urban radiation ring contracts in its southern and western quadrants, whereas it expands in the eastern and northern quadrants. This finding prompts the authors to advocate the city of Zhengzhou to prioritize on expanding its radiation to the southeastern area around the Zhongyuan Urban Agglomeration. Such balanced development could prove beneficial to not only Zhengzhou City, but also the entire Henan Province.