The definition, assessment, and enhancement of urban vitality have always been central themes in urban planning research and practice, playing a crucial role in improving the well-being of residents, achieving efficient governance, and promoting high-quality urban development. The built environment shapes residents’ travel behavior and fosters urban vitality, as confirmed by well-established research evidence. For instance, built environment characteristics such as convenient public transportation networks, provision of green spaces, and diverse land use have all been proven to have a positive association with urban vitality.

Most vitality-related studies have primarily been conducted in medium- or low-density cities in Western contexts, however, research in the context of China, which is one of the world’s fastest urbanizing and densely populated regions, remains relatively underexplored. In addition, China’s current urban development strategies have the megastructure and hierarchical features; often using a central city to stimulate the development of a metropolitan area, using a central metropolitan to stimulate the development of urban agglomeration, and using a central urban agglomeration to stimulate the development of a whole region. Establishing multi-scale research enhances the understanding of urban vitality in the China’s context, offering valuable insights into sustainable urban growth.

As China’s level of urbanization continues to rise, existing research on urban vitality faces three significant challenges: first, the existing research fails to effectively capture the tight connections of different spatial scales and to seize the complex patterns in resident behaviors across neighboring cities (e.g., at urban agglomerations or metropolitan level); second, there is an inadequacy in research examining the spatial disparities in infrastructure, industry, and population distribution within urban agglomeration and metropolitan areas, leading to an incomplete understanding of the regional differences in urban vitality; third, there is no comprehensive indicators that accurately reflect the multidimensional characteristics of urban vitality.

In accordance with the evolving pattern in urban planning, which has shifted from the traditional approach of developing of standalone cities to the development of urban agglomerations and metropolitan areas, this dissertation addresses the core scientific issue of “the impact of built environment on urban vitality from a multi-scale perspective”, focusing on three aspects: 1) What are the spatiotemporal distribution characteristics and influencing factors of urban vitality at the scale of urban agglomerations? 2) How to identify urban vitality gradients at the metropolitan area scale? What are the influencing elements of different urban gradient areas; 3) What are the relationships between urban form and urban vitality at the city center scale? What are the similarities and differences across different cities? Accordingly, a research framework is proposed for studying spatial characteristics and influencing factors of urban vitality on multiple scales in the context of high-density urban settings. The objective is to thoroughly investigate the spatiotemporal distribution and influential factors of urban vitality within high-density urban contexts.

The Pearl River Delta (urban agglomeration scale), the Beijing Commuting Circle (metropolitan area scale), and the corresponding central urban areas of Beijing, Guangzhou, and Shenzhen (city center scale) are selected as three study cases. By integrating multiscale cases, machine learning, and spatial analysis techniques, a framework is constructed to forge vitality spatiotemporal indices and spatial classification methods. This framework accurately depicts the spatial distribution patterns of urban vitality at different spatial scales and analyses the multidimensional impacts of the built environment on residents’ lives.

As shown in the first three chapters, this dissertation delves into the background and literature on urban vitality research, pointing out the general limitations of current research, particularly related to the research of urban agglomerations and metropolitan areas. The dissertation underscores the significance of thorough investigation into the relationship between urban form and vitality. Based on these insights, this study proposes a multi-scale theoretical framework for urban vitality research in order to more deeply understand and promote vibrant urban environments in China’s high-density context.

Chapter Four takes the Pearl River Delta as a case study to extensively explore the spatial and temporal distribution patterns of urban vitality at urban agglomeration scale, by introducing a comprehensive set of indicators of urban vitality, including density, stability, day-night and holiday-workday tidal flows. The analysis reveals clear differences between core and peripheral cities in terms of vitality patterns, with core cities characterized by a high and stable density of vitality, while peripheral cities are marked by a more dispersed vitality with spatiotemporal dynamics. The study demonstrates that road density and the proximity to railway stations exert a significant influence on both the density and stability of urban vitality. And the research establishes a significant correlation between population and GDP densities with urban vitality, while residential POI and NDVI are significantly linked to the stability of urban vitality.

In Chapter Five, the research shifts the focus to the Beijing Commuting Circle. The research systematically categorizes the urban vitality gradient areas and identifies the spatial boundaries of different vitality gradient areas in the Beijing Commuting Circle by utilizing the vitality tidal footprint index. The chapter further employs spatial regression models to analyze the interplay between the built environment and urban vitality of each vitality gradient area. This approach reveals regional disparities between vitality centers and peripheral zones, confirming a positive impact of road density and land use mix on urban vitality across areas with different vitality gradient areas. Moreover, it identifies unique factors influencing urban vitality within different vitality gradient areas.

Chapter Six focuses on the city centers of Beijing, Guangzhou, and Shenzhen as case studies. An automated pedestrian flow detection mechanism is used powered by machine learning technology to analyze over 640,000 street view images for quantifying urban vitality. This chapter introduces interaction terms of built environment variables to evaluate the complex relationship between urban form and vitality. It is found that building height significantly moderates the positive effect of footprint on urban vitality, while the positive moderating effect of road density and urban greening on building density is limited to high-density areas. Although the relationship between the most built environment factors and urban vitality shows consistency across the central regions of Beijing, Guangzhou, and Shenzhen, differences in the factors affecting urban vitality among these cities are still evident, attributed to geographical location, historical background, and economic development levels.

Chapter Seven and Eight synthesize the main conclusions and contributions against the backdrop of urban vitality characteristics at different scales in China’s high-density context, offering multi-scale urban vitality planning and optimization recommendations from different dimensions such as macro-scale comprehensive coordination and network optimization, meso-scale zoning reinforcement and job-housing balance, and micro-scale spatial planning and temporal optimization.

The innovation of this research is manifested in four aspects: First, by constructing a multi-scale vitality assessment framework of “urban agglomeration - metropolitan area - city center”, this study provides new insights into urban vitality the study in China’s high-density context. Second, the innovation in research methods and indicators, including the introduction of vitality stability, tidal effects, and pedestrian flow assessment, enhances the precision and applicability of urban vitality measurements. Third, the development of a vitality gradient methodology improves the understanding of urban-rural differences in urban vitality. Fourth, in-depth analyses of the complex relationship between urban form and urban vitality provide new perspectives on the underlying mechanisms of urban vitality.

The dissertation not only contributes comprehensive perspectives and methodological support to the field of urban vitality but also offers a solid theoretical foundation and practical guidance for the high-quality development of urban and rural areas under the new urbanization strategy. The research findings help promote the transformation of megacities’ development strategies from scale expansion to regional synergy, which emphasizes the unified development of megacities with their neighboring cities to build an efficient commuting circle and a convenient living circle. Moreover, the methodologies and findings of the dissertation may serve as valuable references for urban vitality research in other regions globally.