The Impact Of Population Density And Population Structure On Urban Productivity

China's urban development report in 2017 indicates that since the reform and opening up,the level of urbanization in China has continued to rise,reaching 57.35% at the end of 2016,the urban population has exceeded the rural population,and the city is the main carrier to promote economic development and absorb the transfer of agricultural population.Urban productivity is an important indicator of urban development.When studying urban productivity,the population still plays an important role in it.The fact that population agglomeration promotes productivity has been confirmed by a large number of examples in developed countries.In the United States,the urban area of more than two hundred and forty million people accounts for only 3% of the total land area of the United States,but contributes to the vast majority of the GDP value of theUnited States.This paper selects a total of 3450 samples of 230 cities in 2000-2015 years.Through the fixed effect model,the population size and population structure are placed in the same framework to study the population factors that affect urban productivity.First,the existence of "inverted U" model between population size and urban productivity is tested;then,the focus is from the perspective of the floating population.The impact of urban population flow on urban productivity is analyzed.Finally,the impact of population structure aging on urban productivity,and whether the floating population in cities can reduce this negative impact,thus improve urban productivity.The results show that there is a "inverted U" relationship between population size and urban productivity.When the population size is small,the urban productivity increases with the increase of the population size due to the agglomeration effect and professional division of labor.The productivity of the city will decrease with the increase of population.The flow of population between cities is conducive to the improvement of urban productivity.The positive impact of population inflow on local cities is more negative than that of population outflow;population aging has a negative impact on urban productivity,and the population flow between cities is conducive to reducing the negative impact of urban population age structure changes on urban productivity.Accordingly,the following policy suggestions are put forward: properly regulating the large cities and developing small cities;paying attention to the floating population,increasing the productivity of the local cities by the floating population confirms the demographic dividend effect of the migration of the population,and the government should carry out institutional reform in the aspects of household registration,housing and employment,and to the floating population.We should pay attention to and support the discrimination and psychological defects that face,adjust the industrial structure,develop the third industry,and create the third industry which is more suitable for the elderly to reemployment.