# Vulnerability Analysis of a Multilayer Logistics Network against Cascading Failure
## 2 Methodology and Data  
### The Model  
As cities exist in one or more relationship systems, there is a type of differentiation in their links, and an analysis of the network location of city nodes can start from the links between cities. In terms of spatial organization, a logistics hub city network can be deconstructed into three levels: the physical network of infrastructure, the organizational network, and the trade flow network. Due to the diversification of facility types and organization levels of the physical network, the connection between node cities within the network is accordingly manifested in five forms, including a maritime transportation network, air cargo network, logistics enterprise organization network, international trade network, and integrated logistics network. These five types can be further summarized into two aspects: (1) The connection of the operation trajectory. This form of connection is mainly reflected in the occurrence of marine transportation, air cargo, and other logistics hub cities. Logistics transport between such cities does not rely on the geographic and spatial distribution of the line facilities, and its operational form is mainly expressed in the transport routes of the running track, such as maritime liner routes and air cargo flight routes. The measurement of this relationship is mainly through the number of route flights, frequency, and spatial geographic distribution. (2) The virtual connection of the \"flow relationship\". Such logistics hub cities do not rely on tangible route facilities or invisible trajectory routes but mainly consist of the relationship flows among cities, such as logistics enterprise headquarters branch relationships and international trade relationships. Therefore, this paper selects the maritime transportation network, air cargo network, logistics enterprise organization network, international trade network, and comprehensive network as the main source of research and analyzes the network corresponding to the five types of logistics hub cities: a port-type logistics hub city, air logistics hub city, organization logistics hub city, trade logistics hub city and comprehensive logistics hub city. A city network structured with four distinct layers--Maritime Shipping Network, Worldwide Air-transportation Network, Logistics Enterprise Organization Network, and International Trade Network--reflects the multifaceted and interconnected nature of global urban systems. Each layer serves a unique purpose, and collectively, they form an integrated system facilitating the flow of goods, services, and information. Maritime Shipping Network: This layer represents the global network of seaports and the maritime routes that connect them. It is fundamental for international trade, as the majority of global trade by volume is transported via sea. The maritime network is characterized by its hub-and-spoke system, where major ports act as hubs, and shipping lines connect these hubs to various spoke ports around the world. Worldwide Air-transportation Network: This layer encompasses the global network of airports and air routes. It is crucial for the rapid transportation of high-value goods. The air transportation network is notable for its dense connectivity, especially among major economic centers, and plays a critical role in global economic integration. Logistics Enterprise Organization Network: This layer involves the internal and external logistics operations of enterprises. It includes the coordination of activities such as transportation, storage, and distribution within a company and across its supply chain. The efficiency of this network is key to the competitive advantage of logistics enterprises and the overall performance of the supply chain. International Trade Network: This layer represents the web of trade relationships between cities. It includes the exchange of goods, services, and capital and is indicative of the economic interdependence among cities globally.