  Maritime transport accounts for a majority of trades in volume, of which 70%
in value is carried by container ships that transit regular routes on fixed
schedules in the ocean. In the present paper, we analyse a data set of global
liner shipping as a network of ports. In particular, we construct the network
of the ports as the one-mode projection of a bipartite network composed of
ports and ship routes. Like other transportation networks, global liner
shipping networks may have core-periphery structure, where a core and a
periphery are groups of densely and sparsely interconnected nodes,
respectively. Core-periphery structure may have practical implications for
understanding the robustness, efficiency and uneven development of
international transportation systems. We develop an algorithm to detect
core-periphery pairs in a network, which allows one to find core and peripheral
nodes on different scales and uses a configuration model that accounts for the
fact that the network is obtained by the one-mode projection of a bipartite
network. We also found that most ports are core (as opposed to peripheral)
ports and that ports in some countries in Europe, America and Asia belong to a
global core-periphery pair across different scales, whereas ports in other
countries do not.
