Maritime routes are structured according to the type of commercial service they support, which comes in three main categories:
- Port-to-port. Involves a more or less regular service between two ports, often moving back and forth with unidirectional freight flows involving empty backhauls. This structure has the disadvantage of offering limited connectivity and mainly represents raw materials flows such as oil, minerals, and grain, between zones of extraction and main consumption markets. Chartered ships usually load in one port and discharge their cargo in one to three ports in proximity. Tramp ships (for hire) do not have a specific network structure and service ports according to fluctuations in the demand and the related availability of cargoes.
- Inter-Range. This configuration characterizes containerized cargo and involves a regular itinerary between a sequence of ports where the maritime shipping line seeks to optimize their ship use by electing to service ports having important trade relations. A set of ports along one range (seaboard) is serviced, and then an ocean is crossed, with the process being repeated along a sequence of ports for the other range. The most significant inter-range routes are between East Asia, North America, and Western Europe, the three main poles of the global economy.
- Multi-Ranges. Refer the large long-distance maritime services calling ports along more than two ranges. Round-the-world services call a sequence of ports, often in both directions, so that the sequence involves a circum-equatorial trip around the world. A limited amount of ports per range are serviced. This strictly concerns container shipping and involves a series of transshipment hubs where regional cargo is collected. The term pendulum route is often applied to a maritime service covering three ranges, one of them often intermediary (in between). For instance, a service calling a sequence of ports in East Asia, South Asia, and Europe is considered a pendulum service.