One Country Multiple Urban Systems: focusing on bimodality in China's city-size distribution

Abstract

In this study, we first demonstrate the existence of bimodality in China’s urban hierarchy and then develop an urbanization forecast model that incorporates this bimodality. Main data for our analysis is 0.25º×0.25º population density grids for 32 years between 1954 and 2012, created from China’s official census data and county-level population statistics. Our results show that the mixture of two Gaussian distribution explains China’s historic city-size distribution much better than the single Gaussian distribution. This suggests that the unitary (U-form) urban hierarchy assumption, widely adopted in conventional urban-growth models, does not hold for China, supporting our multidivisional (M-form) hierarchy hypothesis. We also find that the higher-density mixture component increasingly dominates the entire mixture distribution over time, meaning that China’s city-size distribution gradually moves toward unimodality, away from bimodality. This tendency is closely related to increased cross-regional mobility due to China’s loosening domestic migration control.