Structure of Polycentric Circles Based on the Urban Radiation Pattern: A Case Study in the Yangtze River Delta Region, China

Abstract

The metropolitan area is the inevitable trend of urbanization towards an advanced form. The pattern of urban radiation is the key to building a metro area and promoting high-quality regional development. In order to effectively promote the rationalization of metropolitan areas and regional integration development, this paper takes the Yangtze River Delta (YRD) region as an example, calculates the intensity of city centrality (ICC) based on the statistical data, and explores the radiation pattern and spatial relationship of cities at different levels by using methods such as the extended breaking point model and the hierarchical Voronoi diagram. The research results show that: (1) The ICC in the YRD shows a spatial pattern of “high in the east and low in the west, high in the middle and low in the north and south”. (2) The ICC value of “strong-strong” adjacent cities shows the tendency of the radiation range to shrink and that the radiation direction is perpendicular to both sides. The “strong-weak” adjacent cities’ radiation range and direction show an expansion–contraction trend. The radiation range and direction of “weak-weak” adjacent cities exhibit disorder. (3) Because the ICC is hierarchical, urban radiation is a polycentric, nested circle structure. Shanghai is the first-level center, and Hangzhou, Nanjing, Ningbo, Hefei, and Xuzhou are the second-level centers. (4) The sequence of the spatial morphological complexity and stability in each circle, from complex to simple, is the Hangzhou circle, the Shanghai circle, the Xuzhou circle, the Hefei circle, and the Nanjing circle. The spatial morphological characteristics of the Ningbo circle do not meet the morphological dimension conditions. The study of the polycentric circle structure is of practical significance for the enhancement of the radiation driving effect of the central city and the expansion and improvement of the metropolitan area.