"Despite carrying 90 percent of the planet's trade, nobody has mapped the network of links between the world's ports. Until now."

...[T]he maritime network shows some surprising differences from the network that flight paths make between airports. For example, on average, it takes just 2.5 jumps to move from one port to another on the maritime network compared to an average of 4.4 to move between one airport and another. The maximum shortest path between ports is 8 jumps while between airports it is 15 jumps. It looks to be decidedly easier to travel the world by ship than by plane, at least in some respects.

One oddity, however, is that the maritime network is decidedly asymmetric: more than half of all ports are linked in only one direction, meaning that cargo ships do not routinely make round trip journeys between ports.