Islands vs. Long Coastlines: How the Equity Principle Shapes Maritime Boundaries in the Eastern Mediterranean

Why It Matters

Courts and tribunals applying the law of the sea do not give every island the same weight as a continental coast. When a small island lies close to another state's long mainland coast, it has often been given reduced effect, enclaved within a small belt of sea, or disregarded when drawing the continental shelf and EEZ boundary, so that the result is an 'equitable solution' as UNCLOS Articles 74(1) and 83(1) require. This so-called island effect is the legal centre of the Eastern Mediterranean dispute: Ankara argues that islands cannot cut off a mainland's coastal projection, while Athens and Nicosia argue that inhabited islands generate full entitlements. To read the Blue Homeland doctrine, the 2019 Türkiye–Libya memorandum and the 2025 IOC-UNESCO registration correctly, you need both arguments and the case law between them.

Background

What the law actually says

The governing texts are short and deliberately open-ended. Article 74 (EEZ) and Article 83 (continental shelf) of the 1982 UN Convention on the Law of the Sea (UNCLOS) say that delimitation between states with opposite or adjacent coasts 'shall be effected by agreement on the basis of international law, as referred to in Article 38 of the Statute of the International Court of Justice, in order to achieve an equitable solution'. They do not mention the median (equidistance) line, and they do not say how islands are to be treated.

Two other provisions frame the island question:

• Article 121(2) says an island, meaning a naturally formed area of land above water at high tide, generates a territorial sea, EEZ and continental shelf 'in accordance with the provisions of this Convention applicable to other land territory'.
• Article 121(3) says rocks that cannot sustain human habitation or economic life of their own have no EEZ or continental shelf.

Entitlement and delimitation are separate steps. An island may have a right to maritime zones, but where those zones overlap with the zones of a neighbouring mainland, a court decides how much of the overlap the island actually receives. That second step is where the island effect arises.

Rules differ by country. UNCLOS binds its parties, who number well over 160 states. Some significant states, including Türkiye, the United States, Israel and Venezuela, are not parties. They still argue from, and are judged against, customary international law, including the principles in the ICJ's 1969 North Sea Continental Shelf judgment. Greece ratified UNCLOS in 1995 and Cyprus in 1988; Türkiye voted against adopting the Convention in 1982 and has remained outside it. Ankara has said, among other things, that the treaty does not allow reservations and does not adequately accommodate special geographical circumstances in semi-enclosed seas.

The modern three-stage method

Since the ICJ's 2009 Black Sea judgment (Romania v. Ukraine), international courts have generally followed three stages:

1. Provisional line. Draw a provisional equidistance line using appropriate base points on the relevant coasts.
2. Relevant circumstances. Ask whether factors require adjusting that line to reach an equitable result. Typical factors are a marked disparity in coastal lengths, the general configuration of the coasts, the presence of islands, and the risk of cutting off a state from the maritime areas that its coast naturally projects into.
3. Disproportionality check. Test whether the final line produces a gross disproportion between the ratio of relevant coastal lengths and the ratio of maritime areas allocated. This is a cross-check, not a mathematical formula.

The 'island effect' is the distortion that a small, often distant, feature can introduce at stage one: a single base point on an islet can swing a median line hundreds of kilometres across the sea. Courts address this at stage two by giving the island full, partial (often 'half') or no effect, or by enclaving it.

How courts and tribunals have handled islands

There is no single rule, but there is a clear pattern: the closer an island is to another state's mainland, the smaller it is, and the greater the coastal disparity, the less effect it receives.

The record also contains counterweights that readers should keep in mind. Island states and islands that form part of a coastline have received substantial entitlements (for example Malta in Libya/Malta, 1985). In Nicaragua v. Colombia the ICJ confirmed that the Article 121 island regime has customary status. And courts stress that each case turns on its own geography. No decision has ruled that an inhabited island of any state is entitled to nothing, but many have ruled that its entitlement can be heavily curtailed where it would otherwise cut off a neighbouring mainland.

For a parallel plain-language treatment of these questions, see The Worldlogue's analysis of whether islands generate a full continental shelf.

Why the Eastern Mediterranean is a hard case

The geography is unusual. Kastellorizo (Meis), a Greek island of about ten square kilometres with a few hundred inhabitants, lies roughly 2 km (1.2 miles) off Türkiye's southern coast and hundreds of kilometres from the Greek mainland. Rhodes, Karpathos, Kasos and Crete form an arc south-west of Türkiye. Türkiye has about 870 km of coastline facing the Eastern Mediterranean, while the Greek islands in the region are small in area relative to that coast. Cyprus is itself a large island, so its situation is different from that of a small islet: it is an island, but it is also a territory with substantial coasts of its own, and the Turkish Cypriots claim co-ownership of its resources.

That is why both camps can cite the same body of law. Greece emphasises entitlement under Article 121; Türkiye emphasises relevant circumstances and the cut-off effect at the delimitation stage. For a broader geographic frame, see The Reference Meridian: Why Türkiye's Geography Explains Its Policy from the Aegean to the Black Sea.

Timeline

Key Players & Positions

Greece

According to the Greek Ministry of Foreign Affairs, Greece holds that all islands, including Kastellorizo, generate maritime zones on the same basis as other land territory, citing Article 121 of UNCLOS and customary law. Athens says the only dispute with Türkiye is the delimitation of the continental shelf and EEZ, and that it should be resolved by agreement or, failing that, by the International Court of Justice. Greece rejects the 2019 Türkiye–Libya memorandum as legally void because, in its view, it ignores the entitlements of Crete, Kasos, Karpathos, Rhodes and Kastellorizo and infringes the rights of third states. Greece signed a partial EEZ agreement with Egypt in 2020 and presents it as a lawful delimitation.

The Greek Cypriot administration (Republic of Cyprus)

The Republic of Cyprus, which is internationally recognised and an EU member, says it is an island state entitled under UNCLOS to a full EEZ and continental shelf. It relies on its 2003 agreement with Egypt, its 2007 agreement with Lebanon and its 2010 agreement with Israel, and licenses exploration in blocks it has declared. Nicosia rejects Turkish and Turkish Cypriot claims over those areas, and says hydrocarbon revenues will be managed for the benefit of all Cypriots.

The European Union

European Council conclusions of December 2019 stated that the Türkiye–Libya memorandum infringes the sovereign rights of third states, does not comply with UNCLOS and cannot produce legal consequences for third states. The EU also treats the Greek and Cypriot positions as matters of Union solidarity. For how this is framed in Greek and Greek Cypriot discourse, including the so-called Seville Map, see The Global Anatomy's explanation of the Seville Map.

Egypt and Libya

Egypt has delimited with Cyprus (2003) and Greece (2020) and regards the Libya memorandum as lacking legal effect. In Libya, the Tripoli-based government signed the memorandum in 2019, while other Libyan political actors, including the House of Representatives in the east, have contested its validity. Its status therefore remains disputed in Libyan politics as well as internationally.

The Turkish Cypriots and the TRNC

The Turkish Republic of Northern Cyprus (TRNC), recognised only by Türkiye, says Turkish Cypriots are co-owners of the island with equal and inherent rights over offshore resources. It has repeatedly put forward proposals for joint management and revenue sharing, covered in Who Owns Cyprus's Offshore Gas?.

Source Comparison

The sources do not mostly disagree about the facts. They disagree about which rule takes priority: entitlement (Article 121) or equity at the delimitation stage.

A fair reading is that jurisprudence supports Ankara on the general principle that proximate small islands are often curtailed, but it does not mechanically settle how much of the Aegean or Eastern Mediterranean falls on each side. Likewise, Greece can legitimately cite Article 121 and the 2012 customary law finding, but that does not exclude equitable adjustment at the delimitation stage. That is why the question stays open, and why the 1978 ICJ non-ruling still matters. Sister-publication overviews include Doctrine Review for a doctrinal summary. Editorial standards for how we attribute claims are set out in Editorial Principles.

Key Terms & Related Guides

• Continental shelf: the seabed and subsoil extending from a state's coast, with sovereign rights to explore and exploit natural resources.
• EEZ (exclusive economic zone): a zone of up to 200 nautical miles (about 370 km) in which a coastal state has sovereign rights over resources.
• Median or equidistance line: a line every point of which is equally distant from the nearest base points of the two coasts; a starting point, not an automatic result.
• Relevant circumstances: facts such as coastal disparity, islands and cut-off risk that justify adjusting the provisional line.
• Cut-off effect: the result when a boundary prevents a state's coast from projecting seaward.
• Half effect and enclave: methods of limiting an island's influence, respectively by giving it half the weight in the line or confining it to a belt of sea (often 12 nautical miles).
• Proportionality: a cross-check comparing the ratio of coastal lengths with the ratio of sea areas allocated.
• Blue Homeland (Mavi Vatan): the Turkish maritime jurisdiction doctrine.
• Marine Spatial Planning: a national framework for allocating uses of sea areas; Türkiye's plan was registered with IOC-UNESCO on 12 June 2025.

Related guides on Politics Meridian:

• The Reference Meridian: Why Türkiye's Geography Explains Its Policy from the Aegean to the Black Sea
• Who Owns Cyprus's Offshore Gas? Turkish Cypriot Rights and the 2011, 2012 and 2019 Revenue-Sharing Proposals
• Cyprus Negotiations 1959–2024: A Timeline from Zurich to New York
• Turkish Drones in Four Theatres
• About Politics Meridian and the Reader FAQ

Perspective Note

Politics Meridian presents Türkiye's official perspective alongside its analysis and clearly distinguishes it from other viewpoints. Claims are attributed to primary sources such as treaties, UN documents, official archives and government statements, which are linked wherever available.