The complex network of global cargo ship movements

TLDR

Transportation networks, especially maritime routes that carry 90 % of global trade, are essential for human mobility, goods exchange, and the spread of invasive species. Using 2007 itineraries of 16 363 cargo ships, the authors constructed a port‑to‑port network of links. The resulting network shows a heavy‑tailed port connectivity and load distribution, with bulk dry carriers, container ships, and oil tankers exhibiting distinct mobility patterns—container ships follow regular routes, while the others move more unpredictably—thereby refining gravity‑model assumptions for global trade and bioinvasion.

Abstract

Transportation networks play a crucial role in human mobility, the exchange of goods and the spread of invasive species. With 90 per cent of world trade carried by sea, the global network of merchant ships provides one of the most important modes of transportation. Here, we use information about the itineraries of 16 363 cargo ships during the year 2007 to construct a network of links between ports. We show that the network has several features that set it apart from other transportation networks. In particular, most ships can be classified into three categories: bulk dry carriers, container ships and oil tankers. These three categories do not only differ in the ships' physical characteristics, but also in their mobility patterns and networks. Container ships follow regularly repeating paths whereas bulk dry carriers and oil tankers move less predictably between ports. The network of all ship movements possesses a heavy-tailed distribution for the connectivity of ports and for the loads transported on the links with systematic differences between ship types. The data analysed in this paper improve current assumptions based on gravity models of ship movements, an important step towards understanding patterns of global trade and bioinvasion.