How do population inflow and social infrastructure affect urban vitality? Evidence from 35 large- and medium-sized cities in China

Maintaining urban vitality and promoting sustainable urban development is a critical concern because global urbanisation continues to accelerate. This study creates a model to measure urban vitality by means of NPP-visible infrared imager radiometer sensor (VIIRS) nighttime light data and observes that urban vitality and NPP-VIIRS nighttime light data are highly positively correlated, which greatly expands the application of nighttime light data in urban research. This paper further researches the impact of population inflow and social infrastructure on urban vitality by establishing a panel fixed effect model based on the data of 35 large- and medium-sized cities in China to provide new ideas to understand urban vitality from the perspective of public service. The results illustrate that increasing the financial investment of social infrastructure can effectively improve urban vitality, and population inflow influences urban vitality through the interaction effect with social infrastructure. With the inflow population increasing, the educational financial expenditure's positive effect on urban vitality will be enhanced, and the medical and health financial expenditure's positive effect on urban vitality will be suppressed. This paper provides guidance regarding reasonable population inflow and urban vitality improvement.