This article investigates the degree of overlap among the different layers of circulation composing global maritime flows in recent decades.
Physical maritime flows among cities of the world remain a much underexplored area to date.
The resulting tables were merged into one single maritime database, which served to construct a global origin-destination (or adjacency) matrix of inter-port maritime flows.
To date, very few attempts were made to fill such a gap, such as the measurement of cities' global accessibility combining multiple layers of which maritime flows (Nelson 2008), the analysis of combined maritime and airline flows (Parshani et al. 2010), and the analysis of maritime flows in relation to subnational socio-economic features in the Asia-Pacific region (Ducruet and Itoh 2015).
Such a preliminary result already answers, at least partly, the initial hypothesis as a very high proportion of maritime flows concentrate at larger cities.
In other words, larger cities keep dominating global maritime flows, but they have been gradually challenged by smaller ones at the bottom of the urban hierarchy.
Maritime flows of merchant vessels among ports of the world have been recorded by the maritime insurance company Lloyd's List since the late sixteenth century, focusing primarily on the British fleet but since 1890, on any other.
Among all existing maritime data, the Lloyd's List, a world leader in shipping intelligence, is the only possible source capable of documenting the global distribution of maritime flows in a disaggregated manner and over time.
The explosion of computer capacity, the revival of the "science of networks", and the growing availability of maritime traffic data soon gave birth to numerous analyses of global maritime flows, which greatly varied in objectives and outcomes.
Therefore, major opportunities in terms of transport flows development are: a high potential growth of maritime flows to all the most important geo-economic market areas worldwide (thanks to the increase in global competitiveness of EU in certain industries).
