Ports in a World Maritime System: A Multilevel Analysis - Methods for Multilevel Analysis and Visualisation of Geographical Networks - page 124

Fig. 8.1 Scale-free dimension of the world maritime network, 1996-2006 (Source: calculated by
the author based on LMIU)
the figures - a few ports having the fewest connections - are explained by the
methodology of data collection: only twelve ports are not very well-connected to
the rest of the network in both years. In terms of evolution, we note that the slope
of the line and the coefficient have increased from 1996 to 2006, highlighting a
concentration of the network. This result most likely stems from the rationalization
of carrier services, notably through the implementation of hub strategies throughout
the world.
The spatial structure is observable through TULIP software based on the ports'
betweenness centrality that is the sum by port of all their positions on their shortest
paths. This measure is equivalent to a level of relative accessibility within the graph.