Ports serve two functions related to their connectivity to the foreland and hinterland. Centrality refers to how a port is connected to its hinterland and to the economic density of its market. A port with high centrality has a dense, well-connected hinterland, whereas a port with low centrality has a low-density hinterland with limited connections. Centrality tends to be a more stable component of port geography, since economic conditions and the resource density of a hinterland change slowly.
Intermediacy refers to how a port is connected to the global maritime shipping network, particularly in terms of its deviation from the 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.
A port nexus is a location characterized by high centrality and intermediacy, and it is considered the best maritime location 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.