Mapping the hierarchical structure of the global shipping network by weighted ego network analysis

An improved complex network approach named weighted ego network analysis (WENA) was employed to explore the hierarchical structure of the global shipping network. First, it was found that all centrality indices exhibited scale-free properties with obvious power-law distributions. That is, less than 30% of shipping ports had quite high centrality values, which are powerful hubs of the global shipping system. Those very accessible shipping ports showed significant preferential attachment properties such as 'rich-club' and 'Matthew' effect. Second, results of WENA revealed its core-peripheral hierarchical structure, which could be divided into five levels of sub-networks: first tier (top 5%), second tier (top 5%~15%), third tier (top 15%~30%), fourth tier (top 30%~50%), and fifth tier (the remainder). Finally, five kinds of correlation analyses have been carried out, including degree vs. degree, degree vs. strength, degree vs. clustering coefficient, degree vs. distance and centrality vs. GDP. Results indicated that the connectivity of a shipping port was both significantly influenced by the connectivity of its directly connected ports, the shipping distance and hinterland economic scale.