The geographical space of maritime transportation is primarily defined by its absolute barriers. 71% of the earth’s surface is covered by water, dominantly oceanic masses, but the profile of continental masses seriously constrains maritime access to different parts of the world. The maritime system can be summarized by four major oceans representing centers of gravity between elements of the world system (Atlantic, Pacific, Indian and Mediterranean) and seven interoceanic passages representing intermediate locations between these oceanic masses. They are all strategic locations within the maritime space, particularly the bottlenecks at the nexus of major interoceanic passages.