Law on Drawing Baselines

Law on drawing baselines

1. Background to the law

The seas and oceans of the world had long been subject to the freedom-of-the-seas doctrine. This was a principle put forth in the seventeenth century with a view mainly to limiting national rights and jurisdiction over the seas and oceans to a narrow belt of sea surrounding a nation’s coastline. The remaining sea and ocean space was proclaimed to be free to all states and belonging to none.

Apart from a few instances of violation of this centuries-old principle during armed conflicts, it continued to be honoured well into the twentieth century. However, for a number of political and economic reasons, especially those surrounding the Second World War, by mid-century there was an impetus to extend national claims over offshore resources. In addition, there was growing concern over the toll taken on coastal fish stocks by long-distance fishing fleets from faraway countries and continents.

Equally, concern was growing about the threat of pollution and waste from transport ships and oil tankers carrying noxious cargoes that plied sea routes across the globe to service the massive industrialisation that followed the Second World War. The hazard of vessel-source pollution was ever present, threatening coastal resorts and marine habitats. In the Cold War that began soon after the Second World War, the navies of the major maritime powers were competing to maintain a presence and influence across the globe on the surface waters and even under the sea.

Developing states in general, and smaller and weaker states in particular, felt threatened and intimidated by the presence of warships and submarines right on their doorstep. All in all, it was a time ofanxiety on the part of many coastal states who wished to gain some additional security by claiming the maritime areas around their coast as their own and excluding or keeping at a distance vessels of all kinds belonging to other nations. All of these developments were posing new challenges to the principle of the freedom of the seas, and they warranted a new legal regime defining the rights and duties of coastal states in the seas and prescribing the limits of various maritime zones. 

It was against this background that UNCLOS III was convened, and the outcome of the Conference was the 1982 Convention, which deals with all major aspects of the seas, including navigational rights, territorial sea limits, economic jurisdiction, the legal status of resources on the seabed beyond the limits of national jurisdiction, the passage of ships through narrow straits, the conservation and management of living marine resources, the protection of the marine environment, a marine research regime and, a more unique feature, a binding procedure for the settlement of disputes between states. New limits of the territorial sea and acceptance of different methods of drawing baselines brought order to conflicting claims.

2. Importance of the drawing of baselines

Drawing of baselines is a crucial activity for any coastal state because the breadth of all other maritime zones, including the territorial sea and the exclusive economic zone (EEZ), begins from such lines. Any column of water within the baselines will be internal waters, and states have full sovereign rights in such waters. There is no right of innocent passage in internal waters except in cases where the application of straight baselines has resulted in the enclosure of sea waters traditionally regarded as part of the territorial sea. These are some of the reasons why other states pay close attention to the method a coastal state uses to draw its baselines.

i)Historical background

Originally, the law and practice on drawing baselines required the drawing of normal baselines following the configuration of the coast.

However, when states with unusual coastlines started to depart from the principle of normal baselines to include sea waters as internal waters off their coasts, the law evolved to respond to such new claims.

The first such case was the Anglo-Norwegian Fisheries Case, in which the UK challenged the special Norwegian method of drawing straight baselines connecting the outer tips of the fjords and fringing islands off the Norwegian coastline. In a landmark judgment, the International Court of Justice recognised the special character of the configuration of the Norwegian coastlines and held that departure from the traditional rule on normal baselines was permissible in special cases. Since then the law of the sea has evolved to respond to claims of a special method of drawing baselines by coastal states with special coastal configurations.

ii)Normal baseline

According to Article 5 of the 1982 Convention on the Law of the Sea, the normal method of drawing baselines is to draw a line along the coast of a state following the low-water line. It reads as follows: 

Article 5

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.

The 1982 Convention takes all sorts of special geographical and historical factors into account and prescribes different methods for drawing special baselines in such cases.

iii)Straight baselines

The 1982 Convention allows states with special or unique coastlines to draw straight baselines. Application of straight baselines is permissible in a number of situations such as deeply indented coastlines, fringing islands and where baselines are unstable because of the presence of a delta. Article 7 of the Convention provides rules on drawing straight baselines as follows:

Article 7

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. 

iv)Other special considerations


Article 6 of the 1982 Convention provides:

Article 6


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.

b)Mouths of rivers

Article 9 of the Convention allows for the drawing of straight baselines across the mouth of a river flowing directly into the sea:

Article 9

Mouths of rivers

If a river flows directly into the sea, the baseline shall be a straight line across the mouth of the river between points on the low-water line of its banks.


The outermost permanent harbour works that form an integral part of the harbour system are regarded as forming part of the coast. However, off-shore installations and artificial islands shall not be considered as permanent harbour works.

d)Rule on bays

Bays occupy a special place in the law of the sea. For a number of historical and geographical reasons, the law has come to admit a set of special rules on drawing baselines on bays belonging to a single state. When prescribing rules on drawing baselines on bays, Article 10 of the 1982 Convention provides a definition of bays to which the rules apply. The normal rules on bays do not apply to the so-called ‘historic’ bays, for which separate considerations apply.

Definition of a bay

According to Article 10(2) of the Convention:

“2. …a bay is a well-marked indentation whose penetration is in such proportion to the width of its mouth as to contain land-locked waters and constitute more than a mere curvature of the coast. An indentation shall not, however, be regarded as a bay unless its area is as large as, or larger than, that of the semi-circle whose diameter is a line drawn across the mouth of that indentation.”

v)Method of drawing baselines on a bay

Articles 10(4) and (5) of the Convention contain the main provisions concerning the method of drawing baselines on a bay in the following words:

4. If the distance between the low-water marks of the natural entrance points of a bay does not exceed 24 nautical miles, a closing line may be drawn between these two low-water marks, and the waters enclosed thereby shall be considered as internal waters.

5. Where the distance between the low-water marks of the natural entrance points of a bay exceeds 24 nautical miles, a straight baseline of 24 nautical miles shall be drawn within the bay in such a manner as to enclose the maximum area of water that is possible with a line of that length.

vi)Archipelagic baselines

According to the 1982 Convention, an ‘archipelagic state’ means a state constituted wholly by one or more archipelagos and may include other islands. An ‘archipelago’ means a group of islands, including parts of islands, interconnecting waters and other natural features which are so closely interrelated that such islands, waters and other natural features form an intrinsic geographical, economic and political entity, or which historically have been regarded as such.

Article 47 of the Convention provides that an archipelagic state may draw straight archipelagic baselines joining the outermost points of the outermost islands and drying reefs of the archipelago, provided that within such baselines are included the main islands and an area in which the ratio of the area of the water to the area of the land, including atolls, is between 1:1 and 9:1. 

The article reads as follows:

Article 47

Archipelagic baselines

  1. An archipelagic State may draw straight archipelagic baselines joining the outermost points of the outermost islands and drying reefs of the archipelago provided that within such baselines are included the main islands and an area in which the ratio of the area of the water to the area of the land, including atolls, is between 1 to 1 and 9 to 1.
  2. The length of such baselines shall not exceed 100 nautical miles, except that up to 3 per cent of the total number of baselines enclosing any archipelago may exceed that length, up to a maximum length of 125 nautical miles.
  3. The drawing of such baselines shall not depart to any appreciable extent from the general configuration of the archipelago.
  4. Such 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 where a low-tide elevation is situated wholly or partly at a distance not exceeding the breadth of the territorial sea from the nearest island.
  5. The system of such baselines shall not be applied by an archipelagic State in such a manner as to cut off from the high seas or the exclusive economic zone the territorial sea of another State.
  6. If a part of the archipelagic waters of an archipelagic State lies between two parts of an immediately adjacent neighbouring State, existing rights and all other legitimate interests which the latter State has traditionally exercised in such waters and all rights stipulated by agreement between those States shall continue and be respected.
  7. For the purpose of computing the ratio of water to land under paragraph l, land areas may include waters lying within the fringing reefs of islands and atolls, including that part of a steep-sided oceanic plateau which is enclosed or nearly enclosed by a chain of limestone islands and drying reefs lying on the perimeter of the plateau.
  8. The baselines drawn in accordance with this article shall be shown on charts of a scale or scales adequate for ascertaining their position. Alternatively, lists of geographical coordinates of points, specifying the geodetic datum, may be substituted.
  9. The archipelagic State shall give due publicity to such charts or lists of geographical coordinates and shall deposit a copy of each such chart or list with the Secretary-General of the United Nations.

The sovereignty of an archipelagic state extends to the waters enclosed by the archipelagic baselines. It extends to the airspace over the archipelagic waters, as well as to their bed and subsoil, and the resources contained therein. The 1982 Convention requires that archipelagic states designate ‘archipelagic sea lanes’ that allow nearly full freedom of navigation under the regime of transit passage in international straits.

vii)Summary and conclusions

These rules on drawing baselines are now widely regarded as part of customary international law that is binding on all states, whether they are party to the Convention or not. This complex set of rules has evolved out of state practice and the decisions of international courts and tribunals. Since the geographical situations of different coastal states vary a great deal, the 1982 Convention allows coastal states flexibility to determine their baselines by applying any of the methods provided for in the Convention to suit different conditions.

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