The global shipping network is the worldwide network of maritime traffic. From a network science perspective ports represent

node In general, a node is a localized swelling (a "knot") or a point of intersection (a vertex). Node may refer to: In mathematics *Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two or more curves, lines, ...

s and routes represent

lines Line most often refers to: * Line (geometry), object with zero thickness and curvature that stretches to infinity * Telephone line, a single-user circuit on a telephone communication system Line, lines, The Line, or LINE may also refer to: Arts ...

. Transportation networks have a crucial role in today's economy, more precisely, maritime traffic is one of the most important drivers of global trade.

History

90% of world trade is transported on water and in 2012, the most heavily trafficked sea route saw ships travel predominantly from China to the West Coast of the United States.

The network science perspective

As with every network, maritime traffic can be also viewed through a network scientist's glass. Ports can be regarded as nodes and the paths ferries travelling on are the lines. If this network is just as any other like railway or airport networks, one can have valid statements about its operation. The ocean's traffic system also has its routes, gateways, some of which functioning as a major hub or interconnection. A paper by Kaluza et al.Kaluza, P., Kölzsch, A., Gastner, T., Blasius, B.

010 010 may refer to: * 10 (number) * 8 (number) in octal numeral notation * Motorola 68010, a microprocessor released by Motorola in 1982 * 010, the telephone area code of Beijing * 010, the Rotterdam Rotterdam ( , , , lit. ''The Dam on the R ...

br>"The complex network of global ship movements"
J.R. Soc. Interface, pp.1093-1103 investigates cargo ship movements on real data. They use data on all major ports and the largest ships, that can be regarded as the majority of the shipping transport – it contains 93% of the total world capacity of cargo ship transport. Here, "each trajectory can be interpreted as a small directed network where the nodes are ports linked together if the ship travelled directly between ports". The weights of the links between i and j ports are the potential space of the ships travelling between them.

Asymmetry

The global directed ship network's prominent characteristics is that it is asymmetric – as 59% of the linked pairs have only one direction. The routes are short – there is no need for a lot of steps to get from one port to another, as the

average path length Average path length, or average shortest path length is a concept in network topology that is defined as the average number of steps along the shortest paths for all possible pairs of network nodes. It is a measure of the efficiency of information ...

is 2.5, with maximum of 8 and 52% of the pairs can be connected by two steps. This is much more fewer than in the case of

airport An airport is an aerodrome with extended facilities, mostly for commercial air transport. Airports usually consists of a landing area, which comprises an aerially accessible open space including at least one operationally active surface ...

networks as both the average and the maximum are significantly higher: 4.4 and 15 respectively. (Guimera et al.{{cite journal , last1 = Guimerá , first1 = R. , last2 = Mossa , first2 = S. , last3 = Turschi , first3 = A. , last4 = Amaral , first4 = L.A.N. , year = 2005 , title = The worldwide air transportation network: anomalous centrality, community structure, and cities' global roles , journal = Proc. Natl. Acad. Sci. USA , volume = 102 , issue = 22, pages = 7794–7799 , pmc=1142352 , pmid=15911778 , doi=10.1073/pnas.0407994102, arxiv = cond-mat/0312535 , bibcode = 2005PNAS..102.7794G , doi-access = free )

Clusters

The shipping network is highly clustered, its

clustering coefficient In graph theory, a clustering coefficient is a measure of the degree to which nodes in a graph tend to cluster together. Evidence suggests that in most real-world networks, and in particular social networks, nodes tend to create tightly knit groups ...

is 0.49, which can be interpreted that any given node's neighbors are also connected to each other. The average number of links of a node is 76.5, which is much higher as opposed to the airport network, that is 19.4. These facts show that shipping networks are denser, which also gives a higher robustness to it. As many real-world networks it also has the property of having a lot of nodes with only a few links but some having extremely lot of links. Although it is not exactly a scale-free network, the distribution of link weights follows a

power law In statistics, a power law is a Function (mathematics), functional relationship between two quantities, where a Relative change and difference, relative change in one quantity results in a proportional relative change in the other quantity, inde ...

. The distribution of the nodes strength (average link weights arriving and departing from port i) also follows a power law, which means that only a few ports manage immense amounts of cargo.

Betweenness centrality

Betweenness centrality In graph theory, betweenness centrality (or "betweeness centrality") is a measure of centrality in a graph based on shortest paths. For every pair of vertices in a connected graph, there exists at least one shortest path between the vertices such ...

is another important concept. It is basically the sum of the directed paths in the network that pass through a particular node. Ports with high betweenness are quite important. Such nodes are the

Panama Panama ( , ; es, link=no, Panamá ), officially the Republic of Panama ( es, República de Panamá), is a transcontinental country spanning the southern part of North America and the northern part of South America. It is bordered by Cos ...

and Suez canals or

Shanghai Shanghai (; , , Standard Mandarin pronunciation: ) is one of the four direct-administered municipalities of the People's Republic of China (PRC). The city is located on the southern estuary of the Yangtze River, with the Huangpu River flow ...

and

Antwerp Antwerp (; nl, Antwerpen ; french: Anvers ; es, Amberes) is the largest city in Belgium by area at and the capital of Antwerp Province in the Flemish Region. With a population of 520,504,

Different subnetworks

There are also differences between the main ship types:

container ship A container ship (also called boxship or spelled containership) is a cargo ship that carries all of its load in truck-size intermodal containers, in a technique called containerization. Container ships are a common means of commercial intermodal ...

s, bulk dry carriers and

oil tanker An oil tanker, also known as a petroleum tanker, is a ship designed for the bulk transport of oil or its products. There are two basic types of oil tankers: crude tankers and product tankers. Crude tankers move large quantities of unrefined crud ...

s. These differences reflect to the fact that they follow distinctive traffic patterns. While container ships typically follow set schedules with fixed path for a regular service, dry carriers change their routes more often. Furthermore, container ships are much faster than the other categories - average days spent in the port is 1.9 in contrast to 5.6 of bulk dry carriers or 4.6 of oil tankers. The proper kind of ports also affect the properties of the possible network.

References

Maritime transport Network theory