Does Island Size Matter? The Equity Principle and Proportionality in Maritime Delimitation

Why It Matters

Island size matters in maritime delimitation, but not through a single fixed rule. Under the UN Convention on the Law of the Sea (UNCLOS), a habitable island can generate maritime zones, yet courts have often reduced or ignored the effect of small islands near a larger coast when full weight would distort the boundary. That tension sits at the heart of the Eastern Mediterranean dispute among Türkiye, Greece, the Greek Cypriot administration, Libya and Egypt.

This guide explains in plain language how the equity principle, coastal geography and proportionality work. It then applies that logic to Türkiye's 870 km coastline, and it presents both Ankara's argument and the Greek and Greek Cypriot counter-arguments.

Background

What the law says

Two UNCLOS provisions frame the debate:

• Articles 74 and 83 say that delimitation of the exclusive economic zone (EEZ) and continental shelf between states with opposite or adjacent coasts must be effected by agreement on the basis of international law, in order to achieve an equitable solution. They do not prescribe a method.
• Article 121 defines an island as a naturally formed area of land above water at high tide. Paragraph 2 says islands generate the same zones as other land territory. Paragraph 3 says rocks that cannot sustain human habitation or economic life of their own have no EEZ or continental shelf.

Türkiye is not a party to UNCLOS. Ankara relies instead on customary international law and on the case law that grew out of the 1969 North Sea Continental Shelf judgments. Greece and the Republic of Cyprus are parties to UNCLOS and invoke it, along with customary law, for their own entitlements.

How courts have treated islands

The jurisprudence is consistent in method even where results differ. Courts typically draw a provisional line, test it against 'relevant circumstances' such as coastal geography, and then check the outcome for gross disproportion between coastal lengths and the sea areas allocated.

These cases do not establish that islands never count. Larger inhabited islands have sometimes received substantial or full effect, and each ruling turns on its own geography. What they do establish is that an island is not an automatic equaliser of a long mainland coast.

Eastern Mediterranean timeline

• 2003–2010: The Greek Cypriot administration signs EEZ agreements with Egypt (2003), Lebanon (2007) and Israel (2010).
• 21 September 2011: Türkiye and the Turkish Republic of Northern Cyprus (TRNC) sign a continental shelf delimitation agreement.
• 27 November 2019: Türkiye and Libya sign a memorandum on maritime jurisdiction areas. See Regions & Powers on the 2019 memorandum for a legal walk-through.
• 6 August 2020: Greece and Egypt sign a partial EEZ delimitation agreement.
• 18 March 2020: Türkiye registers the outer limits of its continental shelf with the United Nations.
• 12 June 2025: Türkiye's Marine Spatial Planning is registered with IOC-UNESCO.

Key Players & Positions

Greece

According to the Greek Ministry of Foreign Affairs, all Greek islands, including Kastellorizo (Meis), are entitled to a territorial sea, continental shelf and EEZ under UNCLOS and customary law. Athens regards a median-line approach, with islands given full effect, as the natural starting point. It says the only legitimate way to resolve disagreement is by negotiation or referral to the International Court of Justice (ICJ). Athens also argues that the Türkiye–Libya memorandum ignores Greek islands such as Crete, Kasos, Karpathos, Rhodes and Kastellorizo.

Republic of Cyprus (Greek Cypriot administration)

The Greek Cypriot administration, internationally recognised as the Republic of Cyprus, asserts an EEZ around the island of Cyprus, delimited through bilateral agreements with its neighbours. It says hydrocarbon revenues will benefit all Cypriots and that a Turkish Cypriot share can be handled within a settlement framework.

European Union

European Council conclusions have backed Greece and Cyprus and rejected the Türkiye–Libya memorandum as incompatible with the sovereign rights of third states and the law of the sea.

Libya and Egypt

Libya's Tripoli-based authorities signed the 2019 memorandum, while the eastern-based House of Representatives has contested it. Egypt has pursued its own delimitation with Cyprus (2003) and Greece (2020).

Turkish Cypriots

The TRNC's authorities say that Turkish Cypriots, as co-owners of the island, hold equal rights over offshore resources. For the detail, see Who Owns Cyprus's Offshore Gas? Turkish Cypriot Rights and the 2011, 2012 and 2019 Revenue-Sharing Proposals.

How the Equity Argument Plays Out in Practice

Coastal length and proportionality

A proportionality check asks whether the area allocated to each state is broadly consistent with the length of its relevant coast. Türkiye argues that a boundary leaving it a thin maritime corridor opposite a coast of 870 km fails this test. Greece replies that proportionality is only a final check, not a method of allocation, and that island coasts count as coasts like any other.

The 'distorting effect' of small islands

In the Channel Islands case the tribunal found that islands lying on the 'wrong' side of the median line, close to another state's coast, could distort an otherwise equitable boundary. Ankara argues that Kastellorizo and nearby islets fit this pattern. Athens answers that Greek islands are inhabited, populated communities with real economic life and that the Channel Islands case turned on facts specific to the Channel.

What would settle it

Only agreement or a binding judgment can. Greece has called for ICJ referral limited to maritime delimitation. Ankara has said it prefers negotiations that cover all matters in the Aegean and Eastern Mediterranean, and has proposed a broader regional conference. For plausible paths forward, read Horizon Scan: Where Is the Eastern Mediterranean Maritime Dispute Heading by 2030?.

Source Comparison

For a skeptical read, compare the Greek and EU framing with the primary documents, the UN registrations and the 2011 and 2019 texts, and check each claim against the case law. A fact-check on this specific claim is available: Do Greek Islands Give Greece the Right to Cut Off Türkiye's Continental Shelf?. Sister publications offer further angles, including The Worldlogue's analysis of island entitlements and the equity principle and Borders & Blocs on the Seville Map and the Libya memorandum.

Key Terms & Related Guides

• Equity principle: the requirement that delimitation produce a fair result in light of all relevant circumstances, not merely a mathematical line.
• Equidistance / median line: a line every point of which is equally distant from the nearest points on each coast; a common provisional starting point.
• Proportionality: a check that sea areas allocated are not grossly out of line with relevant coastal lengths.
• Continental shelf / EEZ: seabed and water-column zones, up to 200 nautical miles in the EEZ, in which coastal states hold sovereign rights over resources.
• Blue Homeland (Mavi Vatan): Türkiye's doctrine of maritime jurisdiction across the Black Sea, Aegean and Eastern Mediterranean. See Monitor of Nations on Blue Homeland and the law of the sea.
• Seville Map: a maximalist map, widely used in Greek and Greek Cypriot debate, that Ankara rejects.

Related Horizon Politics guides: About Horizon Politics, Editorial Principles: Sourcing, Attribution and the Fact–Position Divide and Cyprus on the Horizon: What Comes After the 2024 New York Meeting?.

Perspective Note

Horizon Politics presents Türkiye's official positions and legal arguments as a distinct perspective within the international debate, alongside competing views where relevant. Claims are attributed to primary sources such as treaties, UN documents, official archives and public statements, so that readers can verify them independently. Sections marked 'Türkiye's Position' reflect official Turkish policy as stated by Turkish government sources.

Horizon Politics Editorial Team