While centrality focuses on the terminal as a point of origin and traffic destination, intermediacy focuses on the terminal as a transit point between different circulation systems. The concept of centrality is straightforward, as the vicinity (hinterland) of the terminal is either the origin or the destination of the movement, which in turn is linked with the level of economic activity. The extent of this vicinity remains to be fully assessed, but a range of about 100 km appears suitable as it corresponds to a commuting or drayage range. Intermediacy, however, is a multifaceted concept that relates to several issues:
- Range. A conventional aspect of intermediacy that tends to be less important today. Due to technical limitations of the modes, such as the range of an aircraft or the need to refuel a coal-powered ship, intermediate locations were used as stages to overcome the range gap, as two locations could not be reached in a single trip. Intermediate airports such as Anchorage, Alaska (transpacific flights) or Gander, Newfoundland (transatlantic flights) are good examples of locations that were used to overcome the technical limitations of aircraft before the introduction of long-range wide-body aircraft. Although range plays a more limited role in air passenger transportation, it remains prevalent in air freight transportation, as freight aircraft have a narrower range due to heavier loads. Therefore, transpacific air cargo routes commonly involve a stop at Anchorage, while Asia-Europe routes will stop at a Middle Eastern airport such as Dubai. To a lesser extent, intermediate locations are used for long-distance trucking, since drivers require rest periods, but the required facilities are very basic.
- Gateway. Connects two systems of circulation and thus represents an intermediate location imposed by geographical constraints. Thus, to reach its final destination, a movement must use an intermediate location, often requiring a transfer from one mode to another. Many gateways also have a significant centrality component as they represent industrial zones and large urban agglomerations.
- Hub (Interception). A location nearby, or at the convergence of several long-distance routes, can develop an intermediacy by “intercepting” some of the traffic. This is notably the case for intermediate hub terminals along major long-distance maritime corridors, such as Algeciras (Spain) or Singapore.
- Hub (Transcalar). A location is specifically used to connect different scales of a transport system. Air transportation is a notable example of the emergence of hub-and-spoke network structures, in which hubs serve as intermediate locations for regional and international flights. Freight distribution, particularly cross-docking distribution centers, relies on intermediate locations to service specific market segments often supplied by distant sources.