UNCLOS Maritime Baselines

A maritime baseline is the legally recognised coastal reference line from which a State measures the seaward extent of its maritime zones. Under UNCLOS, 1982, the usual reference is the normal baseline, namely the low-water line shown on officially recognised large-scale charts.

Types of baselines

UNCLOS adapts the baseline to different coastal configurations while limiting artificial extension of maritime claims.

• Under Article 5, the normal baseline follows the low-water line along the coast.
• Under Article 7, straight baselines may join appropriate coastal points where the coast is deeply indented or has a fringe of islands in its immediate vicinity.
• UNCLOS also provides special rules for river mouths and bays under Articles 9 and 10, and for archipelagic States under Article 47.

How baselines determine maritime zones

Baselines provide the starting point for drawing outer maritime limits and help distinguish waters under different legal regimes.

• Waters on the landward side of the baseline are generally internal waters, over which the coastal State exercises sovereignty.
• The territorial sea may extend up to 12 nautical miles, and the contiguous zone up to 24 nautical miles, from the baselines.
• The exclusive economic zone may extend up to 200 nautical miles from the baselines.
• Under Article 76, distance from the baselines is also relevant to determining the continental shelf, although its outer edge may extend beyond 200 nautical miles where prescribed geological and distance criteria are satisfied.

Baselines and boundary delimitation

A baseline determines the extent of a State's potential maritime claim, but it does not by itself settle overlapping claims between neighbouring States.

• For opposite or adjacent coasts, territorial-sea delimitation is governed by Article 15, subject to historic title or special circumstances.
• Delimitation of overlapping exclusive economic zones and continental shelves is undertaken under Articles 74 and 83 to achieve an equitable solution.
• Because the normal baseline is tied to the low-water line, coastal erosion and sea-level rise can create uncertainty when coastlines and official charts change.