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Baseline (sea)

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Title: Baseline (sea)  
Author: World Heritage Encyclopedia
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Subject: United Nations Convention on the Law of the Sea, Internal waters, Territorial waters, Ambalat, Fjords and channels of Chile
Collection: Hydrography, Law of the Sea
Publisher: World Heritage Encyclopedia

Baseline (sea)

A baseline is the line from which the seaward limits of a state's territorial sea and certain other maritime zones of jurisdiction are measured. Normally, a sea baseline follows the low-water line of a coastal state. When the coastline is deeply indented, has fringing islands or is highly unstable, straight baselines may be used.


  • Measurement of baseline 1
    • Normal baseline 1.1
    • Reefs 1.2
    • Straight baselines 1.3
  • See also 2
  • Notes 3
  • References 4

Measurement of baseline

Chilean Baseline

The following methods are used to measure a baseline under United Nations Convention on the Law of the Sea 1982.

Normal baseline

Except where otherwise provided in this Convention, the normal baseline for measuring the breadth of the territorial sea is the low-water line along the coast as marked on large-scale charts officially recognized by the coastal State.[note 1]


In the case of islands situated on atolls or of islands having fringing reefs, the baseline for measuring the breadth of the territorial sea is the seaward low-water line of the reef, as shown by the appropriate symbol on charts officially recognized by the coastal State.[note 2]

Straight baselines

  1. In localities where the coastline is deeply indented and cut into, or if there is a fringe of islands along the coast in its immediate vicinity, the method of straight baselines joining appropriate points may be employed in drawing the baseline from which the breadth of the territorial sea is measured.
  2. Where because of the presence of a delta and other natural conditions the coastline is highly unstable, the appropriate points may be selected along the furthest seaward extent of the low-water line and, notwithstanding subsequent regression of the low-water line, the straight baselines shall remain effective until changed by the coastal State in accordance with this Convention.
  3. The drawing of straight baselines must not depart to any appreciable extent from the general direction of the coast, and the sea areas lying within the lines must be sufficiently closely linked to the land domain to be subject to the regime of internal waters.
  4. Straight baselines shall not be drawn to and from low-tide elevations, unless lighthouses or similar installations which are permanently above sea level have been built on them or except in instances where the drawing of baselines to and from such elevations has received general international recognition.
  5. Where the method of straight baselines is applicable under paragraph 1, account may be taken, in determining particular baselines, of economic interests peculiar to the region concerned, the reality and the importance of which are clearly evidenced by long usage.
  6. The system of straight baselines may not be applied by a State in such a manner as to cut off the territorial sea of another State from the high seas or an exclusive economic zone.[note 3]

See also


  1. ^ Article 5 (UNCLOS 1982)
  2. ^ Article 6 (UNCLOS 1982)
  3. ^ Article 7 (UNCLOS 1982)


  • United Nations Convention on the Law of the Sea (UNCLOS) – Part II
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