Geostrategy relates to the role of geography as a facilitator or constraint to maritime shipping, which is associated with the selection of specific routes and the conditions for their use. This mainly relates to the effects of physical and political geography:
- Physical geography. The most fundamental factors concern the contour of oceanic masses, which impose a strictly defined domain of maritime circulation, underlining the importance of chokepoints. Bathymetry is also an important factor since it influences navigational capabilities, particularly port access. This has become even more complex with the growth in ship size, inciting ports and waterways managers to undertake capital-intensive drayage and harbor improvements to improve accessibility. Climate can have a determining effect, particularly during the winter, when ice can block whole areas to navigation or impair its use.
- Political geography. Concerns the complex array of factors related to political decisions concerning whether ships are allowed to transit through an area under national jurisdiction. Although international conventions allow for free navigation for commercial purposes, access to ports is subject to the agreement of the concerned nations. Trade policy, including tariffs and quotas, indirectly influences shipping networks by facilitating or constraining trade. There is a wide range of international and national rules and regulations, particularly covering fuels, emissions, labor conditions, security and safety, and cabotage. An important agreement concerns Exclusive Economic Zones (EEZs), allowing nations to access marine resources within a 200-nautical-mile buffer without preventing the freedom of navigation. Geopolitical tensions, piracy, and conflicts can be associated with embargoes, restrictions, and even the blockage of maritime shipping routes.