Taiwan's Maritime Zones: Baseline, Territorial Sea, Contiguous Zone & EEZ

In short

Maritime zones are a series of bands measured seaward from a territorial baseline under UNCLOS: the territorial sea (12 nm), contiguous zone (24 nm), and exclusive economic zone (200 nm). The farther offshore, the more limited the coastal state's rights and the greater other states' freedoms. This site can overlay the baseline and 12/24 nm bands, but those lines are an approximate analysis aid, not an official legal delimitation.

Origin: every width is measured seaward from the territorial baseline.
Which zone a ship is in shapes the legal meaning — and suspiciousness — of its behavior.

RELATED → Enforcement Research Glossary Methodology

A ship sits 13 nautical miles off Taiwan's coast — just outside the territorial sea, yet well inside the contiguous zone. Is it "in Taiwan's waters"?

The answer depends on a few invisible lines, all drawn outward from a single baseline.

What Are Maritime Zones and the Territorial Baseline?

The UN Convention on the Law of the Sea (UNCLOS) divides the ocean by distance from shore into bands with different legal status. The starting point is the territorial baseline — usually the low-water line along the coast (the normal baseline), or, where the coast is broken or fringed with islands, straight baselines joining appropriate points.

The key point: the widths of the territorial sea, contiguous zone, and EEZ are all measured seaward from this baseline, not from the shoreline itself. The farther out, the more limited the coastal state's rights and the greater other states' freedoms of navigation and cable-laying.

Four Zones, From Inside Out

Territorial baselineThe line every width is measured from. Not a "zone" itself, but the measuring datum.

Territorial sea (12 nm)Under the coastal state's sovereignty, much like land territory; foreign ships have only the right of "innocent passage."

Contiguous zone (24 nm)The coastal state may exercise the control needed over customs, fiscal, immigration, and sanitary matters to prevent or punish breaches committed within its territory or territorial sea.

200

Exclusive economic zone (200 nm)The coastal state has sovereign rights over natural resources such as fisheries and minerals; but other states keep the freedoms of navigation, overflight, and submarine-cable laying.

One Line to RememberThe closer to the baseline, the more the coastal state has the final say; the farther out, the closer to "high-seas freedom." The contiguous zone and EEZ are not territory — a ship entering them is usually still acting lawfully.

How This Site Uses These Zones

On this site's live map you can overlay the territorial baseline and the 12 nm (territorial sea) and 24 nm (contiguous zone) bands offset from it. These layers help you:

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Read a vessel's position in contextSee at a glance whether a ship is hugging the edge of the territorial sea, deep in the contiguous zone, or still offshore.

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Cross-reference cables and jurisdictionOverlaying cable routes with the zones highlights questions like "which jurisdiction does this cable actually fall in?"

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Support threat assessmentThe same loitering means something different inside the territorial sea or near a cable than out on the high seas.

Legal Delimitation vs Analysis Aid

This must be said plainly: the baseline and 12/24 nm bands drawn here are an approximate visualization computed from public data, meant to aid understanding and risk assessment — not an official legal delimitation.

Real maritime boundaries involve precise basepoint coordinates, agreements and disputes between neighboring states, and are usually fixed by official charts and treaties. This site's lines may differ from official boundaries and imply no sovereignty claim or border position. Treat them as a "reference grid to think with," not a "legal boundary marker."

Why It Matters for the Gray Zone

Maritime zones matter because where a ship is, and what it does there, determine the legal meaning and suspiciousness of its behavior. A foreign ship transiting the high seas is unremarkable; but loitering at low speed inside the territorial sea, or lingering repeatedly in the contiguous zone near a cable route with AIS switched off, is a completely different alert level.

That is the cleverness of gray-zone tactics: they often deliberately work the blurry edges of these lines, never plainly crossing over yet continuously applying pressure. Overlaying vessel tracks with the zones is exactly how this site turns "position" into "risk context."

Data Limitations & Disclaimer

The baseline and 12/24 nm bands here are approximate and are not an official legal delimitation; they imply no sovereignty or border claim.
Actual maritime boundaries depend on official charts, basepoint coordinates, and inter-state agreements, and may differ from these layers.
A vessel being in a given zone is not itself unlawful; suspiciousness depends on behavior, context, and other indicators.
This page is for research and education, aggregating public data under the MIT License.

FAQ

What is a territorial baseline?

The territorial baseline is the line from which each zone's width is measured. It usually follows the coast's low-water line (the normal baseline), or joins appropriate points as straight baselines where the coast is broken or has offshore islands. Every zone's width is measured seaward from this baseline.

What's the difference between the territorial sea, contiguous zone, and EEZ?

The territorial sea (12 nm) is under the coastal state's sovereignty; within the contiguous zone (24 nm) the state may exercise the control needed over customs, fiscal, immigration, and sanitary matters; the EEZ (200 nm) gives the state sovereign rights over natural resources, while other states keep the freedoms of navigation and cable-laying.

Are the zones on this site's map official boundaries?

No. The baseline and 12/24 nm bands are drawn approximately from public data for visualization and risk analysis. They are not an official legal delimitation and imply no sovereignty or border claim.

How do maritime zones relate to gray-zone monitoring?

Which zone a vessel is in shapes the legal meaning and suspiciousness of its behavior. A foreign ship loitering inside the territorial sea, or lingering anomalously in the contiguous zone or near a cable route, warrants more caution than one transiting the high seas. This site overlays vessels with the zones as a supporting lead for threat assessment.

Sources & Methodology

The legal definitions on this page follow the UN Convention on the Law of the Sea (UNCLOS), cross-referenced with the relevant domestic laws of Taiwan (ROC):

UNCLOS: Art. 3 (12 nm territorial sea), Art. 5 (normal baseline), Art. 7 (straight baselines), Art. 33 (24 nm contiguous zone), Art. 55–57 (200 nm EEZ). UN DOALOS full text →
Law on the Territorial Sea and the Contiguous Zone of the ROC and the Law on the Exclusive Economic Zone and the Continental Shelf of the ROC, plus the baseline/basepoints announced by the Executive Yuan. ROC Laws & Regulations Database (English) →

How this site's layers are builtThe baseline uses basepoint coordinates built into the code (territorialBasepoints in map-data.js); the 12/24 nm bands are offset by nautical miles with offsetPolygonNm() and drawn by map-baseline.js. This is an approximation: it does not use an official geodetic datum and does not resolve overlaps or disputes with neighboring states, so it can be off by several nautical miles. It is for visualization and risk assessment only — not an official legal delimitation, and no sovereignty or border claim is implied.

🛰️ Taiwan Gray Zone & Submarine Cable Monitor

Taiwan's Maritime Zones