baseline

In the law of the sea, the baseline is the foundational line of demarcation from which a coastal State measures the seaward breadth of all its maritime zones — the territorial sea, the contiguous zone, the exclusive economic zone (EEZ) and the continental shelf. It is codified principally in Part II of the United Nations Convention on the Law of the Sea (UNCLOS), 1982, building on the earlier Geneva Convention on the Territorial Sea and the Contiguous Zone, 1958, and on the seminal Anglo-Norwegian Fisheries Case (United Kingdom v. Norway), ICJ 1951, which first validated the straight-baseline method in international law. The waters lying landward of the baseline constitute internal waters (Article 8), over which the State exercises full sovereignty, while the zones measured seaward are subject to the graduated rights UNCLOS prescribes.

UNCLOS provides two principal methods. The normal baseline under Article 5 is the low-water line along the coast as marked on large-scale charts officially recognised by the coastal State. Where the coastline is deeply indented or fringed with islands, Article 7 permits straight baselines joining appropriate points, provided they do not depart appreciably from the general direction of the coast and the sea areas enclosed are sufficiently linked to the land to be subject to the regime of internal waters. Special rules govern particular features: Article 6 (reefs), Article 9 (mouths of rivers), Article 10 (bays, including the 24-nautical-mile closing-line and the historic-bay exception), Article 11 (harbour works), Article 13 (low-tide elevations) and Article 47 (archipelagic baselines for archipelagic States such as Indonesia and the Philippines). Critically, the breadth of the 12-nautical-mile territorial sea (Article 3), the 24-nm contiguous zone (Article 33) and the 200-nm EEZ (Article 57) are all reckoned outward from this baseline.

Named practice illustrates its stakes. India has declared straight baselines along stretches of its coast and asserts maritime zones under the Maritime Zones Act, 1976. China's straight baselines around the Paracels and its expansive claims figured in the South China Sea Arbitration (Philippines v. China), PCA 2016, where the tribunal held that low-tide elevations and submerged features generate no territorial sea and rejected baselines drawn around scattered features as inconsistent with UNCLOS. As of 2026, contested baseline claims — including over the Gulf of Sidra, the Spratlys and various Arctic straits — remain live flashpoints, and rising sea levels have prompted debate over whether baselines, once lawfully established, should be "fixed" rather than ambulatory.

For the exam, baseline appears squarely in International Law and Maritime Law sections (UPSC optional and GS, FSOT, CSS International Law). Typical question angles ask candidates to distinguish normal from straight baselines, to identify which UNCLOS article governs a given coastal feature, to compute the outer limit of a zone from a stated baseline, or to explain the holdings of the Fisheries Case (1951) and the South China Sea Arbitration (2016). Precision on article numbers and the 12/24/200-nm thresholds is what separates a model answer from a vague one.