## 2 Literature Review
Complementing these perspectives, [PERSON]'s notion of _Zwischenstadt_ (in-between cities) captures the hybrid spatiality of such zones, which transcend conventional urban-rural divides and embody diverse land-use configurations shaped by regional transportation networks and governance ambiguity [25]. Together, these studies ground the theoretical reimagining of interstitial spaces as complex, dynamic, and integral components of the urban system rather than peripheral anomalies. The rapid urbanization of China and its distinctive institutional contexts have significantly contributed to the emergence of indigenous theoretical perspectives on interstitial urbanization. Many cities have emerged at the boundaries of metropolitan cores, experiencing administrative fragmentation despite strong functional integration with nearby urban centers. This phenomenon has drawn significant interest from Chinese scholars, who have systematically examined these interstices through the multidimensional analyses of their spatial delineation, structural characteristics, functional attributes, and evolutionary dynamics. [PERSON] (2000) first introduced the influential concept of \"metropolitan shadow regions\" based on empirical evidence from the Yangtze River Delta. He demonstrated how administrative barriers and hierarchical governance structures resulted in \"polarization-shadow effects\", wherein higher-tier urban centers exert suppressive impacts on neighboring lower-tier areas, effectively restricting their developmental potential [9]. Building on these ideas, [PERSON] further examined how urban interstitials in the Beijing-Tianjin-Hebei region could evolve into \"developmental opportunity windows\" under favorable conditions. [PERSON] argued that, while these regions often faced administrative fragmentation, they also held significant potential for growth if they could leverage infrastructure investments and favorable policies. His work highlighted the transformative potential of these regions, which could bridge the gap between core cities and peripheral areas [40]. In addition to these foundational studies, [PERSON] et al. quantitatively explored the effects of administrative boundaries on the mobility of developmental factors in Chinese urban regions. They identified administrative fragmentation as a key barrier to regional integration and the flow of human capital, economic resources, and technological innovation between cities. Their research highlighted the need for more coordinated governance strategies to facilitate the functional integration of urban interstices into broader urban systems [7]. Technological advancements in data collection have also played a significant role in the development of urban interstice research in China. [PERSON] pioneered an innovative multidimensional identification framework for interstitial spaces using mobile signaling data and POI (point of interest) big data. [PERSON]'s research introduced a dual-dimensional model combining population mobility and commercial activity patterns, which enabled a more nuanced understanding of the spatial and functional characteristics of urban interstices. His research was instrumental in shifting the focus from purely qualitative analysis to a more empirical and data-driven approach to studying urban interstitials [28]. Similarly, [PERSON] et al. explored how local land policies and industrial distribution gradients contribute to differentiated morphological development patterns within the interstitial areas of Chinese megacities, reinforcing the importance of administrative governance in shaping spatial outcomes [41]. Such research underscores the fact that urban interstices are not passive recipients of metropolitan spillovers, but dynamic development frontiers that are actively shaped by policy gradients and economic processes. In the specific Chinese institutional context, the emergence and growth of interstitial urban areas are strongly influenced by administrative jurisdictions, governance fragmentation, and targeted policy interventions.