# Network Structure and Synergy Characteristics in the Guangdong-Hong Kong-Macao Greater Bay Area
## 2 Literature Review  
With globalization, city clusters are transforming from mere geographic agglomerations into complex functional systems that encompass economic, cultural, and social resources. Through the cross-regional flows of information [8], transportation, capital [9], technology [10], and other factors [11], these clusters create highly interconnected regional networks that enhance their positions in the global value chain. The cooperation and competition among cities accelerate resource flows, serving as a key driver of regional and national economic development. The theory of flow space posits that cities no longer function as isolated units; instead, they are intricately linked to the external environment through multidimensional factor flow [7], particularly within global supply chains, international trade, and multinational enterprises. Consequently, the study of city development must transition from traditional static spatial analysis to a dynamic network perspective, emphasizing how cities integrate into broader regional and global systems through mobility. This approach aims to deepen the understanding of city clusters' functions and identify strategies to enhance overall competitiveness through regional synergy. Research on regional spatial structures and synergies, driven by the combination of flow space and big data, has become increasingly intensive. This research focuses on the following areas:  
(1) Interregional transportation flow refers to the movement of key mobility elements--such as vehicles, goods, people, and information--across geographic regions [12]. As the most visible expression of spatial mobility, transportation flows constitute a fundamental driver of urban development and regional connectivity. From the perspective of research progress and the research paradigm of transportation flow elements, the topological characteristics of transportation networks form the basis for understanding transportation flows. Researchers have used complex network theory to analyze transportation network structure [13]. [PERSON] and [PERSON] [14] demonstrated that transportation networks exhibit scale-free network characteristics, meaning the degree distribution of nodes in the network follows a power law. This characteristic makes transportation networks highly connected [15], which significantly affects their efficiency and reliability [16]. In terms of urban evolution, transportation networks and spatial development are tightly interlinked: denser inter-city transport links lead to more accelerated urban expansion and greater spatial reach [17]. The degree of regional connectivity both within and beyond the urban system shapes regional spatial structures and inter-city relationships [18]. Additionally, transportation flows induce a spatial-temporal compression effect, catalyzing transformations in urban morphology, functional configurations, developmental trajectories, and the spatial dynamics of regional tourism. (2) Intercity interactions are fundamentally anchored in economic linkages, with enterprises serving as key agents within these networks [19]. Under the influence of value law and incentive mechanisms, enterprise-driven investment connections give rise to capital and economic flows that reflect the intensity and tightness of interurban relations [20]. As a critical vector of economic activity, capital flow exerts profound effects on regional development, urban morphology, and the functional specialization of firms [21; 22]. With the advancement of research on transportation and economic factor flows--particularly within the framework of network analysis--scholars have increasingly examined their synergistic interplay from multidimensional perspectives [23]. Empirical evidence indicates a causal feedback mechanism between transportation circulation and economic mobility, forming a closed-loop dynamic [24; 25]. Transportation infrastructure fosters economic vitality, which in turn enhances and sustains transportation systems.