Ports are part of two functions related to their connectivity to their foreland and hinterland. Intermediacy relates to how a port is linked to the global maritime shipping network, particularly in terms of its deviation from main shipping lines. A port with a high deviation (low intermediacy) requires a substantial deviation. It commonly acts as a feeder, while a port with a low deviation (high intermediacy) does not require a deviation and can act as a hub (intermediary) port. Intermediacy can be an unstable component of port geography as shipping networks and trade flows can change.
Centrality relates to how a port is linked to its hinterland and the economic density of its market. A port with a high centrality has a dense and well-connected hinterland, while a port with a low centrality has a low-density hinterland with limited connection. Centrality tends to be a more stable component of port geography since the economic conditions and the resource density of a hinterland are slow to change.
A port nexus represents a location characterized by high centrality and intermediacy, representing the best maritime locations in the world. Ports such as Shanghai, Hong Kong, Busan, Tokyo, Los Angeles, New York, and Rotterdam have high maritime connectivity and substantial hinterlands. There are also pure hub ports, such as Panama, Freeport, Colombo, and Gioia Tauro, with high maritime connectivity but poor hinterlands.