中国城市的人口规模合理吗?——基于2020年人口普查的再探究

Are Chinese Cities too Small or too Big?——Evidence from the 2020 Population Census

本文基于中国2020年人口普查、夜间灯光及各类社会经济指标,并且利用最新文献中运用大数据聚类算法界定的城区空间范围,精准地测度了当前中国212个主要城市城区的实际人口规模。在此基础上实证估计了单体城市人均产出水平与人口规模之间的倒U形关系,并对中国各城市人口规模合适度及相应的以人均GDP度量的效率损失进行了测算。结果表明:尽管过去十年中国城市系统的人口规模总体在扩张,但仍有80%以上的城市人口规模偏小;与此同时,少数超特大城市人口过多的现象突出。规模不合理造成的效率损失明显,有29%的城市损失超过50%。本文进一步探讨了优化城市规模的路径,发现劳动力和资本等要素市场的一体化有利于促进城市规模合理化。本文的研究深化了对当前中国城市系统规模分布的规律性认识,丰富了未来优化城市布局的思路。

Summary:Using China's 2020 population census combined with POI and commuting data,this paper measures the population size within the spatial boundary of urban core area for each of the prefecture level cities in China.We measure the corresponding GDP of urban core area with the help of nightlight data.We then investigate the relationship between cities'GDP per capita and population size thus defined.Following Au and Henderson(2006)and Baum-Snow et al.(2017),we use cities'historic social-economic conditions and Bartik measure as IVs.We find there exists a significant and robust inverted-U relationship between a city's GDP per capita and its population size.Furthermore,such an inverted-U relationship varies with both cities'economic structure and spatial structure,which means that each city has a unique optimal size of population under which the city's GDP per capita reaches maximum given its current economic structure and spatial structure.Specifically,our empirical findings suggest that if a city has a higher share of tertiary industry relative to secondary industry,or if it has a larger R&D output captured by patent value,the city tends to have a larger optimal size of population because such a city has greater potential of agglomeration economies.On the other hand,if a city has a bad spatial structure,then the city tends to have a smaller optimal size of population because such a city is more likely to suffer from urban crowdedness and longer commuting time that cancels off the positive effect of agglomeration economies.We then calculate the gap between each city's actual size and its optimal size inferred from our estimation,as well as the efficiency losses in terms of GDP per capita due to its deviation from the optimal size.The results show that:although in general Chinese cities have been expanding in the past decade,there are still more than 80%of the cities in our sample having population sizes significantly smaller than their respective optimal levels in 2020;by contrast,some mega cities such as Beijing and Shanghai are significantly oversized and too densely populated.The efficiency losses caused by either undersize or oversize are remarkable;about 29%of our sample cities have a loss exceeding 50%of the potential GDP per capita they could generate under optimal size.This paper also explores how to improve the city size distribution of China.We examine the correlation between the deviation of each city's actual size from its optimal size and the factor market integration in the province where the city is located.Specifically,we measure the degrees of integration of both the regional labor market and the regional capital market in 2010,which is ten years before 2020.We find that both increased migration easiness and enhanced capital market integration are negatively correlated with the gap between a city's actual population size and its optimal size(in absolute value).This may suggest that the integration of factor markets such as labor and capital markets can help achieve a more reasonable city size distribution in China.Finally,as an attempt to evaluate cities'welfare instead of just GDP per capita,we construct a utility measure of representative worker for each city using both the city's GDP per capita and its air quality,following Freeman et al.(2019).We then investigate the relationship between the utility level thus calculated and city size.Again we find a significant inverted-U relationship.Moreover,from the point of view of utility level,while there are a large number of Chinese cities are undersized,a few megacities are oversized.The results are qualitatively similar to the previous main results based on GDP per capita.Our paper makes the following four contributions to the literature.First,our study is conducted based on more accurately measured population living in urban core areas,which utilizes China's most recent population census data combined with POI and commuting data.We find that while a large number of Chinese cities are undersized,a few megacities are significantly oversized.The efficiency loss from either under-size or oversize is big.Second,we attempt to address an important policy question:How to improve the population size distribution of the Chinese urban system?Our study suggests that the integration of regional factor markets can help achieve a more reasonable city-size distribution for China.Thirdly,in addition to urban industrial structure,we find that the urban spatial structure is also very important to the fulfillment of the potential of agglomeration economies and hence influences the optimal city size.Finally,we construct a utility measure that incorporates both GDP per capita and the environmental quality and investigate the relationship between this more comprehensive welfare measure and city size.