Macroscopic patterns of global maritime flows
Global trade growth has inevitably resulted in a regular increase in the number of ports and vessels since the late nineteenth century (Figure 1a). Yet the number of inter-port links and vessel calls has fluctuated much more widely (Figure 1b). Over the last 125 years, three peaks of global maritime activity have coincided with periods of relative economic prosperity and great and the large-scale diffusion of technological innovations: steam shipping (1890- 1925), diesel engines (1960-1970) and massive containerships (1985-present). The reduction of links and calls since 1990 underlines the effects of network rationalisation associated with growing vessel sizes, further sailing distances, and an increased concentration of services on fewer ports. The latter trend is confirmed by the evolution of network indices (Figure 2). The average shortest path length has increased relatively fast in recent times which implies a lesser ease of circulation across the network. A similar evolution is illustrated by the power-law exponent, as fewer ports concentrate a larger numberof links over time. In parallel, the regular decline of the Gini index and clustering coefficients suggest an increasing centralisation of the shipping network around large hubs, which are becoming more numerous. The morphology of the global maritime network is increasingly a star-shaped structure whereby a few large hubs dominate a majority of peripheral nodes, as in a typical hub-andspoke system centered upon large and multifunctional distribution platforms. The spread of containerisation has also accelerated rather than disrupted ongoing trends of network evolution. This suggests a strong path and place-dependency of technological change because already established ports have a higher probability to sustain their dominance and to grow than other ports.
Regional shifts in the global port hierarchy
Important changes are felt geographically (Figure 3). Among world regions, there is a clear shift from Euro/Atlantic to Asia/ Pacific dominance. Asia exhibited growth from 6% to 38% of global vessel calls in the 1890 – 2008 period, reaching the highest number of vessel calls in 1995. In 2008, Europe goes back to the initial share of world calls it had back in 1890 (about 35%) after a period of overwhelming dominance marked by strong traffic fluctuations, which lasted until 1970 and was followed by stagnation and rapid decline.