Downloaded from rsif.royalsocietypublishing.org on November 19,2012 6 Compler network of ship movements P.Kaluza et al. (a) ⑥ (c) Figure 3.Communities of ports in three cargo ship subnetworks.The communities are groups of ports that maximize the number of links within the groups,as opposed to between the groups,in terms of the modularity Q(Leicht Newman 2008).In each map,the colours represent the c distinct trading communities for the goods transported by (a)container ships(c=12,Q= 0.605),(b)bulk dry carriers (c=7,Q=0.592)and (c)oil tankers (c=6,Q=0.716).All modularities Q of the examined net- works differ significantly from modularities in Erdos-Renyi graphs of the same size and number of links(Guimera et al.2004). For the networks corresponding to (a),(b)and (c),values are QER=0.219,QER=0.182 and QER=0.220,respectively. characteristics per individual ship (table 1).The aver- (1.9 days on average in our data)in the ports for age number of distinct ports per ship (N does not cargo operations.By contrast,bulk dry carriers and differ much between different ship classes,but con- oil tankers move more slowly (between 13 and 17 tainer ships call much more frequently at ports than knots)and stay longer in the ports (on average 5.6 bulk dry carriers and oil tankers.This difference is days for bulk dry carriers and 4.6 days for oil explained by the characteristics and operational tankers). mode of these ships.Normally,container ships are The speed at sea and of cargo handling,however,is fast (between 20 and 25 knots)and spend less time not the only operational difference.The topology of J.R.Soc.Interfacecharacteristics per individual ship (table 1). The aver￾age number of distinct ports per ship kNl does not differ much between different ship classes, but con￾tainer ships call much more frequently at ports than bulk dry carriers and oil tankers. This difference is explained by the characteristics and operational mode of these ships. Normally, container ships are fast (between 20 and 25 knots) and spend less time (1.9 days on average in our data) in the ports for cargo operations. By contrast, bulk dry carriers and oil tankers move more slowly (between 13 and 17 knots) and stay longer in the ports (on average 5.6 days for bulk dry carriers and 4.6 days for oil tankers). The speed at sea and of cargo handling, however, is not the only operational difference. The topology of (a) (b) (c) Figure 3. Communities of ports in three cargo ship subnetworks. The communities are groups of ports that maximize the number of links within the groups, as opposed to between the groups, in terms of the modularity Q (Leicht & Newman 2008). In each map, the colours represent the c distinct trading communities for the goods transported by (a) container ships (c ¼ 12, Q ¼ 0.605), (b) bulk dry carriers (c ¼ 7, Q ¼ 0.592) and (c) oil tankers (c ¼ 6, Q ¼ 0.716). All modularities Q of the examined net￾works differ significantly from modularities in Erdo¨s –Renyi graphs of the same size and number of links (Guimera` et al. 2004). For the networks corresponding to (a), (b) and (c), values are QER ¼ 0.219, QER ¼ 0.182 and QER ¼ 0.220, respectively. 6 Complex network of ship movements P. Kaluza et al. J. R. Soc. Interface Downloaded from rsif.royalsocietypublishing.org on November 19, 2012