How sensitive are measures of polycentricity to the choice of ‘centres’? A methodological and empirical exploration

In the literature dealing with measuring ‘urban polycentricity’, relatively little attention has been paid to the identification of what constitutes an ‘urban centre’. In this paper, we assess the sensitivity of polycentricity measures to one particular aspect of this identification: using the case of ‘polycentric urban regions’, we empirically examine the sensitivity of the ‘level’ of polycentricity to the number of cities included in the analysis. Using a two-mode firm–city data source, we do so by stepwise measuring the polycentricity of the Yangtze River Delta (YRD) as cities are added to the analysis. This measurement of ‘stepwise polycentricity’ is benchmarked against an ideal typical urban system with a rank-size distribution. The results suggest that the measure of polycentricity is indeed highly sensitive to the choice of the number of cities, so that the alleged level of polycentricity is contingent on the choice of a cut-off point. We propose that the analysis of the sensitivity of polycentricity can help researchers to (1) investigate the different role of cities in shaping polycentric structures of urban regions, and (2) better identify mono- or polycentric structures of urban regions. Analyses of trends in the ‘stepwise polycentricity’ of the YRD and seven other urban regions along the Yangtze River Economic Belt serve to illustrate. 在测量“城市多中心性”方面的文献中，对于识别“城市中心”的构成的关注相对较少。在本文中，我们评估多中心度量对这种识别的一个特定方面的敏感性：使用“多中心城市区域”的一些例子，我们实证检验多中心“水平”对分析中包含的城市数量的敏感性。我们使用双模式城市数据来源，在测量长江三角洲（YRD）多中心性时逐步将各个城市添加到分析中来，以验证这种敏感性。这种“逐步多中心”测量以具有等级大小分布的理想典型城市系统为基准。结果表明，多中心度量确实对城市数量的选择高度敏感，因此所谓的多中心水平取决于选择的截止点。我们提出，对多中心敏感性的分析可以帮助研究人员（1）研究不同城市在塑造城市区域多中心结构中的不同作用，（2）更好地识别城市区域的单中心或多中心结构。作为例证，我们对长江三角洲地区和长江经济带沿线七个城市地区“逐步多中心”的趋势进行了分析。