In economic theory, vertical integration involves an entity, such as a manufacturer, trying to acquire or take control of the upstream activities or downstream of the stage it is involved in. So, a manufacturer may try to acquire some of its suppliers or the distributors or retailers it is selling to. Horizontal integration involves acquiring entities that perform a similar function either as a process of consolidation or for market penetration.
A port authority is a good example of a vertically integrated structure that provides a wide array of services connecting the foreland and the hinterland. If inland facilities such as inland (dry) ports and corridors are developed, port regionalization is emerging. Port holdings, such as Hutchison Ports or DP World, are attempts at horizontal integration by acquiring stakes at port terminals in a variety of markets. A maritime shipping company that ventures into the management of port terminals performs concomitantly a process of vertical and horizontal integration since it is expanding geographically but also from maritime towards inland services (e.g. Maersk – APM Terminals). In all cases, the outcome is a more integrated and efficient transport chain that includes maritime shipping, port terminal operations, inland access, and even freight distribution centers (as a service to customers). If inland facilities such as inland (dry) ports and corridors develop, port regionalization is emergent.