Centrality and Intermediacy
While centrality focuses on the terminal (its vicinity) being a
point of origin and destination of traffic, intermediacy focuses on
the terminal being a point of transit between different systems of
The concept of centrality is straightforward as the vicinity
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 a number of issues:
- Range. This is more a conventional aspect of intermediacy
that tends to be of lesser importance in the contemporary situation. 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 aircrafts before the introduction of
long range couriers. Although range plays a more limited role for
air passenger transportation, particularly with long range
aircrafts, it is still prevalent for air freight
transportation as the range of freight aircrafts is more limited
due to heavier loads. Therefore, transpacific air cargo routes commonly
involve a stop at Anchorage while Asia-Europe routes will have a
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. It 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 have also 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
terminals located along major long distance maritime corridors,
such as Algeciras (Spain) or Singapore.
- Hub (Transcalar). A location is specifically used to
serve as a connection between different scales of a transport system.
Air transportation is a notable example with the emergence of
network structures where the hub is an intermediate location between
regional and international flights.
Freight distribution, particularly cross-docking distribution centers,
also rely on the usage of intermediate location to service specific
market segments often supplied by distant sources.