While centrality focuses on the terminal being a point of origin and traffic destination, intermediacy focuses on the terminal being 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 for air passenger transportation, it is still prevalent for air freight transportation as the range of freight aircraft is more limited 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 rest periods are required for drivers, but the required facilities are very basic.
- Gateway. Connects two systems of circulation and thus represents an intermediate location imposed by geographical constraints. Thus, in order to reach its final destination, a movement must use an intermediate location, often implying a transfer from one mode to the other. 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 between different scales of a transport system. Air transportation is a notable example of the emergence of hub-and-spoke network structures where the hub is an intermediate location between 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.