AP® Human Geography · Unit 4 · Topic 4.5
Maritime Boundaries and the Law of the Sea
The Law of the Sea gives coastal countries layered rights over the ocean: full sovereignty close to shore, limited enforcement a bit farther out, and exclusive resource rights up to 200 nautical miles. Control weakens the farther the zone sits from land.
A country's border does not stop at the beach. The Law of the Sea, formalized in the UN Convention on the Law of the Sea, sets up three zones that stack outward from the coastline, each with weaker control than the last. Territorial waters reach 12 nautical miles out: here the country has full sovereignty, same as on land, meaning it can enforce any law and control passage. Next comes the contiguous zone, out to 24 nautical miles, where the country keeps narrower rights, mainly enforcement over customs, smuggling, and pollution, but not full sovereignty. Beyond that is the exclusive economic zone, or EEZ, reaching 200 nautical miles, where the country does not own the water itself but holds exclusive rights to the fish, oil, and gas beneath it.
This is why a tiny island can hand its owner an enormous ocean claim. An EEZ is measured from any piece of land, however small, so a single reef or islet generates its own 200 nautical mile circle of resource rights, often covering more sea than the country's entire land area.
The system runs into trouble where coasts face each other across a narrow sea. If two countries are less than 400 nautical miles apart, their 200 nautical mile claims overlap, and international law does not let both claim the full distance. The countries must negotiate a boundary, often an equidistant line splitting the difference. This is exactly what drives the South China Sea dispute, where China, Vietnam, the Philippines, and others claim overlapping EEZs around scattered islands and reefs, turning a boundary question into a fight over fishing grounds and undersea oil.
Key terms
- Territorial waters
- The zone up to 12 nautical miles from shore where a country holds full sovereignty, equivalent to its rights on land.
- Contiguous zone
- The band from 12 to 24 nautical miles offshore where a country can enforce customs, immigration, and pollution laws but lacks full sovereignty.
- Exclusive economic zone (EEZ)
- The zone up to 200 nautical miles from shore where a country holds exclusive rights to fish, oil, and other resources.
- Equidistant line
- A compromise boundary drawn at the midpoint between two coastlines when their EEZ claims would otherwise overlap.
- UN Convention on the Law of the Sea
- The international agreement that defines and sets the distances for maritime zones such as territorial waters and the EEZ.
Watch it explained
- How it worksHow does the Law of the Sea stack territorial waters, the contiguous zone, and the EEZ outward?
- Worked exampleDraw the 12, 24, and 200 nautical mile zones running outward from one coastline.
- Going furtherWhat happens when two countries' 200 nautical mile zones overlap in a narrow sea?
- Ties togetherHow do maritime claims in the South China Sea turn a map into a resource dispute?
Check yourself
End of topic.