The mega-regional unevenness, namely the development gap between cores and smaller cities, has increasingly become a key obstacle for inter-city coordination in China. Scholars tend to focus more on the leading role of the cores in responding to this problem. When the smaller cities are mentioned, their endogenous characteristics and weaknesses are often highlighted, rather than being valued as important nodes embedded in the regional network and the inter-city relations. This paper conceptualizes these smaller players in mega-regional system as “secondary cities” to emphasize their interconnectedness to the cores and embeddedness in the inter-city relations. Based on this, we firstly examine the (trans)formation trends of the core-secondary relations in Chinese mega-regionalization. In this way, we focus on the role of secondary cities by exploring the functional and political positioning in the dynamic regional system. Building on such conceptualization of secondary cities, we construct an indicator system to measure changes of core-secondary unevenness from 2006 to 2023. We find that although mega-regionalization aims to rebalance inter-city relations, secondary cities are still facing challenges of polarization and peripheralization. Finally, we conduct a clustering analysis based on the differences between core and secondary cities regarding economic structure, aiming to explore the differentiated vulnerabilities of various types of secondary cities when confronted with polarization and peripheralization. This paper expands the theoretical scope of secondary cities to provide an innovative analytical perspective for understanding the mega-regional unevenness problems in China. Meanwhile, we also emphasize the potential and value of core-secondary relations in addressing the challenges of secondary cities with the expectation of more targeted policy and planning actions.

Adaptive reuse of industrial heritage can showcase industrial culture and drive urban transformation but faces issues like homogenization, secondary ruins, and long-term adaptation deficits. Research gaps include insufficient analysis of correlations between reuse potential and strategies, and limited generalizability from single-case studies. This study addresses these gaps using Changzhou, China’s industrial heritage, aiming to provide a data-driven analytical framework for industrial heritage reuse potential, to reveal the network of potential indicators, to deconstruct the kernel of multidimensional potentials, to show the regional differentiation characteristics of potentials, and to construct a decision-making basis for typological governance. It draws on a consolidated dataset covering industrial heritage with multi-level protection statuses and a sample of 28 sites, identifies multidimensional indicators, explores their interrelations via Pearson correlation analysis, and extracts five primary dimensions–spatial, cultural, locational, operational, and historical potentials–through Factor Analysis, accounting for 70% of variability across 20 reuse indicators. GIS mapping highlights regional variations of these potentials, aiding targeted governance. Hierarchical Cluster Analysis categorizes industrial sites into six adaptive reuse types: unbalanced development, synergistic development, exemplary leading, canal industrial, functional continuity, and to-be-developed. The potential for adaptive reuse of industrial heritage reflects the dynamic needs of heritage governance, which requires systematic protection of heritage through top-down institutional strengthening, while bottom-up community empowerment opens up resilient renewal pathways for heritage. The framework constructed in this research helps to develop targeted regeneration strategies for industrial heritage based on different potential types to maximize its intrinsic value and enhance its long-term adaptation after adaptive reuse, while remaining generalizable to other regions and supporting policy design for adaptive reuse governance.

Mega-regional planning in China is expected to tackle intra-regional unevenness, namely the development gap between regional core cities and the surrounding secondary cities. However, mega-regionalization processes seem to further increase the centrality of cores and push secondary cities towards greater polarization and peripheralization, as they lose socioeconomic vitality, industrial capacity, and political voice. To reflect on why mega-regions are not fulfilling their role of rebalancing regional urban systems, we conceptualize mega-regionalization as a mechanism to coordinate spatial relations within a territory and build a novel framework to analyze the relations between core and secondary cities. First, we show that visions of mega-regional planning regarding core-secondary relations pursue goals of morphological polycentricity, flow multi-directionality, and functional complementarity. Then, we use thematic analysis to evaluate the policy orientations of mega-regional planning to achieve these goals and extract three policy themes governing core-secondary spatial relations - coexistence, connectivity, and cooperation. These can systematically redefine mega-regional planning mechanisms by giving a central role to the spatial relations between core and secondary cities. Emphasizing spatial relations to conceptualize mega-regional governance allows a novel reflection on the challenges of unevenness grounded in the perspective of secondary cities. This deepens our understanding of governance mismatches that keep ideal visions and policy orientations misaligned when seen from secondary cities. Place, priority, and actor mismatches limit the potential of mega-regionalization to respond to their challenges. This research provides a relational understanding of mega-regions, calling for more attention to secondary cities, and the development of more balanced and sustainable mega-regions.

The governmental initiative of high-quality development (HQD) marks a shift in the Chinese development paradigm from prioritizing speed to prioritizing quality towards comprehensive goals of economic growth, social vitality, innovation capacity, industrial upgrading, regional cooperation, and green transformation. This initiative is increasingly discussed within the framework of mega-regions, with prior studies demonstrating that they are critical arenas for promoting HQD visions. However, unevenness within mega-regions has become an important limitation to this vision. Namely, significant disparities exist between mega-regional core cities and the smaller neighboring cities in most HQD indicators. This paper conceptualizes these smaller players as secondary cities. Based on this, this paper aims to understand and differentiate the specific challenges of secondary cities facing intra-regional unevenness in the context of HQD. We build an evaluation framework and employ the TOPSIS method to evaluate 34 core cities and 180 secondary cities. Then, we introduce typological thinking to develop a meaningful classification of secondary cities based on the results of these evaluations. K-means clustering analysis identifies five secondary city types with similar profiles. The analysis supports the discussion of the characteristics and challenges of each type and may contribute to policy recommendations for a balanced HQD in mega-regional secondary cities.

The settlement space along China’s Grand Canal is an important part of cultural heritage, boasting high value of conservation and inheritance as a museum of local culture in an active state. The paper is aimed at revealing the current situation and satisfaction with the settlement space environment along China’s Grand Canal Tianjin Section from the perspective of resident perception. We set up a structural equation model to perform an empirical analysis of the inherent relation of the components of the settlement space environment along China’s Grand Canal Tianjin Section and the inherent law influencing its current state. The research results show that the ecological factor of life along China’s Grand Canal exerted a positive influence on the ecological factor of production and the path coefficient was 0.344. The ecological factor of life and the factor of accessibility were in a relation of positive influence and the former had the most prominent influence on the latter, with a path coefficient of 0.534, while the path coefficient of the influence of the latter on the former was 0.131. The factor of social culture exerted a positive influence on the ecological factor of life, with the path coefficient being 0.765. The research conclusion analyzed the realistic difficulties of the settlement space environment along China’s Grand Canal, revealed the inherent law between different surveyed factors and provided basic reference for feature extraction, evaluation and optimized development of the settlement space along China’s Grand Canal.

The settlement space along China’s Grand Canal composes an important part of the Canal heritage, has a close bearing on the production and life of the residents there, nourishes rich culture and wisdom and boasts vital value of conservation and inheritance. Due to China’s rapid urbanization and industrialization, the settlements along the canal have been destroyed to some extent and their in-site characteristics urgently need excavation and conservation. Through field investigation, space syntax and GIS analysis, this paper performs quantitative analysis of the in-site characteristics of 18 typical rural settlements there. The findings show that: (1) The settlement space of industry dominant type for commerce and trade is comparatively dynamic and the capacity of topology and integration and the attractive force of the settlement center are stronger. (2) The dynamic scope of the citizens’ everyday traveling in the settlements has the closest correlation with the data of public-service facilities. (3) The settlements along the canal boast multiple, causal and blended in-site phenotype. The research findings provide new standards to categorize the settlements along China’s Grand Canal, paths and methods to explore the characteristics of the settlements and new cognitive perspectives to conserve and renew the settlements along China’s Grand Canal Tianjin Section.

The optimized design of natural lighting for residential buildings can greatly reduce lighting energy consumption and improve indoor environmental quality as well as the physical and mental health of residents. Through the DIALux simulation analysis, this paper analyses the importance of natural lighting factors in the Xi'an residential area and analyses factors such as latitude, date, window position, building aspect ratio, building height and window area. The study found that the winter solstice (December 22) is the most unfavourable day for residential lighting in Xi'an. Considering architectural beauty, building energy savings and natural lighting, the winter solstice is an effective time to calculate the window area of residential buildings in Xi'an. The higher the latitude is, the larger the window area required for the house. From April to August, the influence of latitude on window area is small; from January to April and from August to December, latitude has a greater influence on window area. This paper establishes a regression equation for residential window area in Xi'an and provides calculation tools for architects to use when designing residential windows that provides a reference for the design of residential windows at the same latitude (33° north latitude). Intelligent control strategies are put forward on natural lighting in residential buildings for working class families in this paper. An APP on smart phones is developed to realize the intelligent control of curtains. In accordance with family daily routine, the opening width of curtains is controlled automatically based on room functions and exterior illuminance, through which interior illuminance can be adjusted, indoor environmental quality can be improved and energy consumption of HVAC system can be reduced.