A baseline, as defined by the United Nations Convention on the Law of the Sea, is the line (or curve) along the coast from which the seaward limits of a state's territorial sea and certain other maritime zones of jurisdiction are measured, such as a state's exclusive economic zone. Normally, a sea baseline follows the low-water line of a coastal state. This is either the low-water mark closest to the shore or an unlimited distance from permanently exposed land, provided that some portion of elevations exposed at low tide but covered at high tide (such as mud flats) is within 3 nautical miles (5.6 kilometres; 3+1⁄2 statute miles) of permanently exposed land. When the coast is deeply indented, has fringing islands or is highly unstable, straight baselines may be used.
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