In 2018, the integrated development of the Yangtze River Delta became a national strategy, aiming to break administrative barriers with integrated ideas and measures, and achieve the efficient flow of capital, talents, technology and other essential resources. As the main drive for innovation and knowledge-based economy, the reasonable allocation and orderly migration of talents are conducive to promoting regional integration and achieving high-quality development. Against this backdrop, this study focuses on the migration of university graduates, a vital component of regional talent resource. Based on data drawn from Graduate Employment Quality Report, we demonstrate the spatial patterns of graduate migration in the Yangtze River Delta and reveal the influencing factors underlying their migration by using the geographical detector model. The results show that the migration flow of graduates in the study area basically follows the law of reduction with the increase of distance and hierarchy, and the proportion of graduates who stayed and worked in the region reached 79.72%. The intra-provincial migration pattern is diversified in Jiangsu, Zhejiang and Anhui provinces. Cities with a higher retention rate are located in the "Z"-shaped zone and coastal areas. Shanghai and its nearby cities (Suzhou, Jiaxing, and Nantong) have formed a "high-high" cluster with a high retention rate. Furthermore, the results of factor detector show that innovation factors play a stronger role in affecting graduate migration in the delta region. However, the effect of these innovation factors differs among Jiangsu, Zhejiang and Anhui, with the strongest effect found in Jiangsu, followed by Zhejiang, while the insignificant effect in Anhui. The results of risk detector show that once the level of innovation reaches a certain threshold, its effects on attracting university graduates increase substantially. This study reveals the relationship between the migration pattern of university graduates and regional innovation, which provides theoretical and empirical basis for formulating policies to promote regional talent integration.

From a long-term perspective, innovation is the key driving force for economic growth. Under the background of China's economic transition from high-speed growth to high-quality development, the promotion of the innovation level is one of the important measures to achieve higher-quality economic development. A large number of studies conducted in-depth discussions on the spatio-temporal evolution and driving factors of the innovation development, and found that the inefficient allocation of innovation resources and the imbalance co-opetition relationship had become important factors restricting China's innovation development. Under the background of deepening integration, accurately grasping the innovative interactive relationship of urban agglomerations has important practical significance for promoting high-quality development. The spatial spillover effect is an important manifestation of the interactive relationship among regional innovation development. Based on the prefecture level data from 2000 to 2017 and spatial measurement methods, this paper conducts a multi-angle study on the spatial spillover effects of innovation development in the Yangtze River Delta. The results show that: (1) The innovative development had a significant positive spatial spillover effect of the Yangtze River Delta Urban Agglomeration. Overall, innovative talents, capital investment, economic development, transportation facilities, and opening-up were all important driving factors for innovation development, but different factors show differences in spatial spillover effect. (2) Comparing different regions and different periods, we found that there were significant differences in the spatial spillover effects of innovation development, such as stronger core regions and significantly enhanced temporal evolution. (3) Many studies had shown that the spatial spillover effect of innovation development was significantly affected by distance. This article found that the spillover effect exhibited an "inverted U" evolution characteristic with the increase of distance in the Yangtze River Delta, and the strongest spillover effect was found at a distance of 325 km, which showed that there was an optimal spatial boundary for urban agglomerations from the perspective of innovation. However, the spatial spillover effect fluctuated slowly when the distance exceeded 325 km, which was affected by the relatively balanced distribution of central cities. The research provides a new perspective for identifying the co-opetition relationship of innovation development about urban agglomerations, and has practical guiding significance for promoting the innovation development and deepening integration of urban agglomerations.

In the context of the growing gap between urban and rural development, this paper takes the Yangtze River Delta region as a research case and uses the Entropy method to calculate the development index for the 2008-2018 urban-rural integration and spatial integration, economic integration, social integration and lifestyle integration. And then it uses the Geographic Detector Model to analyze the main influencing factors and evolution characteristics of the level of urban-rural integration. The results show that the development level of urban-rural integration in the study region is characterized by spatial evolution from the "high-low-high" structure to a "Σ"-shaped pattern; from the perspective of the spatial characteristics of the urban-rural integration subsystem, the high value of the development level of spatial integration and the level of social integration presents the spatial pattern of a "Σ" shape, the economic integration development level is characterized as high and low circle structure, and the life integration development level roughly presents the spatial pattern of high in the west and low in the east. Seen from the results of the geographic detector model, the level of economic development, industrial advancement, the proportion of fiscal expenditures on agricultural support, and fiscal decentralization are conducive to the development of urban-rural integration; while the speed of economic development, the deviation of industrial structure, and the proportion of urban-rural infrastructure expenditures are not conducive to the urban-rural integration. From the temporal perspective, government power is gradually weakening, and market power is gradually intensifying.

Digital economy technology plays an increasingly important role in industrial transformation and high-quality economic development. Based on 41 cities of the Yangtze River Delta from 2011 to 2018, this paper analyzes the impact of digital economy on the high-quality development of the integration of the delta region, and creatively constructs an imbalance index of talent flow to explore the adjustment effect of the imbalance of talent flow in the region on the relationship between digital economy and high-quality development. The results show that the high-quality development level and the scale of digital economy in the Yangtze River Delta integration are increasing year by year. The development of digital economy has a positive impact on the high-quality development by improving the production efficiency, circulation efficiency and social convenience. The positive impact of non-core areas is stronger than that of core areas. The imbalance of talent flow will reversely regulate the positive impact of digital economy on the high-quality development, but this impact is only found in the core area of the Yangtze River Delta. In addition, digital economy has a negative spatial spillover effect with economic distance as the weight matrix.

As an important part of new urbanization, ecological urbanization is the concrete practice of ecological civilization concept. Taking 41 cities in the Yangtze River Delta as the research area, this paper constructed an index system of regional ecological urbanization, measured the development level of ecological urbanization from 2000 to 2018, and explored the spatiotemporal evolution characteristics of ecological urbanization and the mechanism of influencing factors. The results show that: (1) The overall level of ecological urbanization in the Yangtze River Delta region shows an upward trend, with high value areas gradually clustering in Zhejiang and low value areas concentrating in Northern Jiangsu and Northern Anhui. The gap of ecological urbanization index among cities is gradually narrowing, and the degree of regional ecological integration is continuously improving. (2) The spatial autocorrelation of ecological urbanization in the region gradually increases, and its spatial evolution is characterized by strong variability, dependence and integration. The spatial variability gradually weakens from west to east, and the dependence gradually increases from northwest to southeast. (3) The influence of financial investment level, income gap between urban and rural areas, industrial development level, land investment intensity, population density and scientific and technological development level on the level of ecological urbanization in this region decreases in turn. Under the comprehensive effect of many factors, the level of ecological urbanization in each city gradually converges. Under the combined effect of many factors, the level of ecological urbanization in each city gradually converges. Strengthening the construction of regional ecological integration and improving the level of regional ecological urbanization is an effective way to build a beautiful China and an inevitable choice to achieve regional high-quality development.

Low-carbon economy is the inherent requirement to achieve high-quality integrated development in the Yangtze River Delta. This paper analyzes the spatiotemporal correlation, allometric growth relationship, and driving forces between economic growth and carbon emissions in the Yangtze River Delta Urban Agglomeration from 2000 to 2017. The findings show that: (1) There exists a positive correlation between economic growth and carbon emissions in the study area, and the overall correlation intensity presents a "V-shaped" fluctuation. From 2000 to 2008, the areas with high correlation intensity were relatively concentrated in Southern Jiangsu, Northern Jiangsu and Central Zhejiang. From 2009 to 2017, the spatial correlation intensity decreased significantly, and generally presented a spatial pattern of "low in the south and high in the north". (2) The allometric variation between economic growth and carbon emissions is dominated by weak economic expansion, and the allometric relationship between economic growth and carbon emissions in most areas has turned from positive to negative. (3) The geo-detector diagnoses that the proportions of secondary and tertiary industries, as well as urbanization and population density are the main factors driving the allometric variation between economic growth and carbon emissions. (4) Multi-scale geographical weighted regression shows that the population density has an significantly negative impact on allometric variation between economic growth and carbon emissions, investment intensity and the intensity of fiscal expenditure have an inhibitory effect, urbanization and consumption level show the effect of first promoting and then offsetting, while the proportions of secondary and tertiary industries, and the carbon sequestration ability show the effect of first inhibition and then promotion.