U.S. Maritime Limits & Boundaries

Maritime limits and boundaries for the United States are measured from the official U.S. baseline, recognized as the low-water line along the coast as marked on the NOAA nautical charts in accordance with the articles of the Law of the Sea. The Office of Coast Survey depicts on its nautical charts the territorial sea (12 nautical miles), contiguous zone (24nm), and exclusive economic zone (200nm, plus maritime boundaries with adjacent/opposite countries).

Select limit or boundary for specific information. Data shown is available for download.

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Dynamic map services are updated whenever we make updates to our data. If you are using maritime boundaries in a web map or as a background for other data, we recommend using our dynamic services, as they will seamlessly update in your application. For information about using dynamic map services, please see the frequently asked questions page (FAQ).

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NOAA depicts the limits of the Three Nautical Mile Line, the 12 nautical mile territorial sea, the 24 nautical mile contiguous zone, the 200 nautical mile Exclusive Economic Zone (EEZ), and the extents of the continental shelf on NOAA Nautical Products. For more information on specific limits see the U.S. Coast Pilot and Maritime Zones and Boundaries pages.

Offshore extent of maritime zones beyond internal waters

Baseline

Generally speaking, the normal baseline is the low-water line along the coast as marked on large-scale charts officially recognized by the coastal State (LOSC art. 5). Special rules for determining the baseline apply in a variety of circumstances, such as with bays, ports, mouths of rivers, deeply indented coastlines, fringing reefs, and roadsteads (LOSC arts. 6-15). Consistent with these rules, the U.S. baselines are the mean of the lower low tides as depicted on the largest-scale NOAA nautical charts. The U.S. normal baselines are ambulatory and subject to changes as the coastline accretes and erodes. NOAA's nautical charts depict the baselines from which the seaward limits of the U.S. territorial sea, contiguous zone, and exclusive economic zone are measured as well as the seaward boundary of the Three Nautical Mile Line and the Natural Resources Boundary, as described below.

Three Nautical Mile Line

The Three Nautical Mile Line, as measured from the territorial sea baselines and previously identified as the outer limit of the U.S. territorial sea, is retained on NOAA charts because it continues to be used in certain federal laws.

Note: Since the "coast line," a term used in the Submerged Lands Act (43 USC Section 1301 et seq.), and the baselines are determined using the same criteria under international law, the Three Nautical Mile Line is generally the same as the seaward boundaries of individual U.S. coastal states under the Submerged Lands Act. There are exceptions; therefore, the Three Nautical Mile Line does not necessarily depict the seaward boundaries of all U.S. coastal states in all circumstances under the Submerged Lands Act.

Natural Resources Boundary

The nine (9) nautical mile (nm) Natural Resources Boundary is the seaward boundary of the submerged lands of Puerto Rico, Texas and the Gulf coast of Florida. It coincides with the inner limit of the U.S. outer continental shelf under the Outer Continental Shelf Lands Act (43 U.S.C. Section 1331 et seq.).

Territorial Sea

Each coastal State may claim a territorial sea that extends seaward up to 12 nm from its baselines (LOSC arts. 3, 4). The coastal State exercises sovereignty over its territorial sea, the airspace above it, and the seabed and subsoil beneath it (LOSC art. 2). Foreign flagged ships enjoy the right of innocent passage while transiting the territorial sea subject to laws and regulations adopted by the coastal State that are in conformity with the Law of the Sea Convention (LOSC arts. 17-26) and other rules of international law relating to such passage.

Contiguous Zone

Each coastal State may claim a contiguous zone adjacent to and beyond its territorial sea that extends seaward up to 24 nm from its baselines (LOSC art. 33(1) & (2)). In its contiguous zone, a coastal State may exercise the control necessary to prevent the infringement of its customs, fiscal, immigration, or sanitary laws and regulations within its territory or territorial sea, and punish infringement of those laws and regulations committed within its territory or territorial sea (LOSC art. 33(1)(a) & (b)). In addition, in order to control traffic in archeological and historical objects, a coastal State may presume that the removal of archeological and historical objects (e.g., underwater cultural heritage) found at sea within its contiguous zone without its approval would result in an infringement of its laws and regulations (LOSC art. 303).

The contiguous zone of the United States includes the waters off of all U.S. coastal states, the Commonwealth of Puerto Rico, Guam, American Samoa, the U.S. Virgin Islands, the Commonwealth of the Northern Mariana Islands and any other territory or possession over which the United States exercises sovereignty. In 1999, the United States claimed a contiguous zone extending from 12 to 24 nm offshore (Presidential Proclamation No. 7219 of August 2, 1999, Contiguous Zone of the United States, 64 Fed. Reg. 48,701 (Aug. 8, 1999)).

Exclusive Economic Zone (EEZ)

Each coastal State may claim an exclusive economic zone (EEZ) beyond and adjacent to its territorial sea that extends seaward up to 200 nm from its baselines (or out to a maritime boundary with another coastal State) (LOSC art. 55). Within its EEZ, a coastal State has: (a) sovereign rights for the purpose of exploring, exploiting, conserving, and managing natural resources, whether living or nonliving, of the seabed and subsoil and the superjacent waters and with regard to other activities for the economic exploitation and exploration of the zone, such as the production of energy from the water, currents, and winds; (b) jurisdiction as provided for in the relevant provisions of the LOSC with regard to the establishment and use of artificial islands, installations, and structures, marine scientific research, and the protection and preservation of the marine environment; and (c) other rights and duties provided for in the LOSC (LOSC art. 56).

(See Presidential Proclamation No. 5030, March 10, 1983.)

Certain U.S. fisheries laws use the term "exclusive economic zone" ("EEZ"). While its outer limit is the same as the EEZ on NOAA charts, the inner limit generally extends landward to the seaward boundary of the coastal states of the U.S. For the seaward limit of the state's jurisdiction under the Submerged Lands Act, please see GIS Data / Shapefiles.

Maritime Zones

The maritime zones recognized under customary international law as reflected in the Law of the Sea Convention (LOSC) include internal waters, the territorial sea, the contiguous zone, the exclusive economic zone, the continental shelf, the high seas, and the Area (see Figure 1). The following zones are depicted on NOAA's nautical charts: internal waters, territorial sea, contiguous zone, exclusive economic zone, and continental shelf. The limits of these zones are subject to modification as depicted on NOAA charts; limits shown on the most recent chart edition take precedence.

Continental Shelf

The continental shelf of a coastal State is comprised of the seabed and subsoil of the submarine areas that extend beyond its territorial sea throughout the natural prolongation of its land territory to the outer edge of the continental margin, or to a distance of 200 nm from its baselines where the outer edge of the continental margin does not extend up to that distance (LOSC art. 76(1)). The extent of the continental shelf can also be limited by a maritime boundary with another coastal State (LOSC art. 76(10)). Where the outer edge of a coastal State's continental margin extends beyond 200 nm from its baselines, the outer limits of its continental shelf are determined in accordance with Article 76 paragraphs 2-7 of the Law of the Sea Convention (LOSC art. 76 (2-7)). The portion of a coastal State's continental shelf that lies beyond the 200 nm limit is often called the extended continental shelf.

Where can I find electronic data of state territorial waters at 3 nautical miles (or 9 nautical miles off of Texas, Puerto Rico, and the west coast of Florida)?

The Bureau of Ocean Energy Management (BOEM) manages and disseminates the Submerged Lands Act federal/state boundaries. The data can be found under "GIS Data / Shapefiles". The Gulf of America dataset is available at "GOAR Geographic Information System (GIS) Data and Maps".

We find that most people who seek this line are actually looking for the
Submerged Lands Act federal/state boundary provided by BOEM.

How are the U.S. maritime limits drawn?

The U.S. maritime limits are projected from a "normal baseline" derived from NOAA nautical charts. A "normal baseline" (as defined in the 1958 Geneva Convention on the Territorial Sea and the Contiguous Zone and Article 5 of the United Nations of the Law of the Sea Convention) is the low-water line along the coast as marked on official, large-scale charts. Since "low-water line" does not reference a specific tidal datum, the U.S. applies the term to reference the lowest charted datum, which is mean lower low water (MLLW).

The maritime limits are created using "envelope of arcs," a method by which one rolls a virtual circle along the charted low water line and selects salient points. These salient points are called "contributing baseline points." Arcs generated from these baseline points are blended together to form a continuous limit line or envelope of arcs.

A geometric diagram showing a coastal landmass and the boundaries for the Marginal Sea and High Sea.

Diagram illustrating the geometric method for determining the limit of the "Marginal Sea" (Territorial Sea) as defined by an "envelope line." The Marginal Sea boundary is 3 nautical miles (Mi.) seaward of the baseline, which is drawn using the arc of a circle with a 3 Mi. radius rolled along the coastline, maintaining constant contact. The area beyond this boundary is designated as the "High Sea."

The U.S. Baseline Committee reviews and approves the limits of all maritime zones on NOAA charts. It gains interagency consensus on the proper location of the baseline, using the provisions of the 1958 Convention on the Territorial Sea and the Contiguous Zone, to ensure that the seaward extents of U.S. maritime zones do not exceed the breadth permitted by international law. Current members of the Committee include the Departments of State (Chair), Commerce (NOAA), Justice, Interior (BOEM), and Homeland Security (Coast Guard), among others.

What initiates updates to the digital U.S. maritime limits and boundaries?

The primary triggers for updates include accretion or erosion of the charted low water line by approximately 500 meters or more, or changes to low tide elevations (e.g., rocks awash) as a result of new hydrographic survey information. The Office of Coast Survey and the Baseline Committee will investigate these changes for new edition chart. There are approximately 12 new editions issued each month, and a small number of these charts depict features that impact the U.S. baseline or maritime limits. The Baseline Committee, which meets four to six times per year, reviews and approved all proposed revisions.

Another trigger for change may be the U.S. ratification of a new treaty with a neighboring coastal State. Some areas for future change include the U.S. waters adjacent to Canada, the Bahamas, Kiribati, Tonga, and the Federated States of Micronesia, to name a few.

How often are digital U.S. Maritime Limits and Boundaries updated?

Depending on the level of change, the Office of Coast Survey may update the digital U.S. maritime limits and boundaries as often as every few months in certain areas. Though we provide both dynamic and static datasets, we recommend using our dynamic data services to ensure the most up-to-date version of the U.S. maritime limits and boundaries. We provide an archive of past update announcements (above) to explain what has changed in each release of the data.

How do I use dynamic web mapping services?

We offer dynamic data is two formats: OpenGIS® Web Map Service (WMS) and proprietary ESRI REST service.

The WMS can be used in various desktop GIS software as well as web mapping applications. The link leads to the GetCapabilities page, which provides easy-to-read, detailed information about the data as well as the necessary link to load the data into a GIS or web mapping application. Open Geospatial Consortium (OGC) provides more information about web mapping services.

For users who prefer to work within the ESRI software environment, we provide an ESRI REST (Representational State Transfer) service. This service can be used in ESRI's ArcGIS Desktop software or in ESRI's free ArcGIS Explorer Desktop. It can also be added as a layer in web mapping services, such as ArcGIS Online.

What information is provided with the dataset?

The dataset includes specific information about each maritime boundary segment. Attributes for the data are:

Boundary ID: a unique identifier of the boundary segment
Region Name: region in which the boundary is located
Type of Feature: features can either be a land boundary (between the U.S. and Canada), a maritime limit, or a maritime boundary between the U.S. and an adjacent or opposite country.
Publication Date: date the digital boundary was published online
Approval Date: date the U.S. Baseline Committee approved the updates
Legal Authority: treaty, agreement, or proclamation granting the government authority to establish the limit or boundary
Agency of Responsibility: federal agency responsible for maintaining the digital data
Note: additional notes about the limit/boundary
Supplemental Information Document: link to metadata about the specific boundary segment. The document supplements the parent metadata record.
Unilateral Claim: some maritime boundary claims have not been agreed upon by all parties. These boundaries are designated as unilateral claims.
Description: specific category of maritime limit/boundary.

Why is the digital product different from the product printed on the chart?

Because of a difference in the chart printing schedule and the digital data update schedule, the digital data and the paper charts might not always be identical. In the event that the digital product and the paper charts differ, the maritime limits and boundaries on the paper charts take precedence.

We find that most people who seek this line are actually looking for the Submerged Lands Act federal/state boundary provided by BOEM (see FAQ #1).

HISTORY OF THE MARITIME ZONES UNDER INTERNATIONAL LAW

FROM THE CANNON SHOT RULE TO UNCLOS

For hundreds of years, the marine environment was free from regulation of fishing, shipping, and resource exploitation. Over time, coastal States (countries) had an increased interest in national security and the enforcement of laws to protect its commerce and marine resources. As a result, a balance was needed to maintain the freedom of navigation that many foreign maritime interests had relied upon. This need for balance is captured in the history of the law of the sea.

The birth of a nation's authority to control its coastal waters has been traced back to the sixteenth century. In the seventeenth century, the father of international law and doctrine on the freedom of the seas, Grotius, recognized the existence of a nation's jurisdiction over the coastal waters that could be effectively controlled from the land. The extent to which a nation could control its coastal waters was largely based on the reach of its cannons on the shore. Thus, the 3 nautical mile (nm) limit of the territorial sea resulted from what is often referred to as the "cannon shot" rule. In the U.S., the creation of a territorial sea and contiguous zone date back to as early as the late 1700s in response to issues of national security and law enforcement at coastal areas, including a 1793 diplomatic note sent from Thomas Jefferson and legislation passed by Congress in 1799 to allow the boarding of foreign flag vessels within 12 nm from the coast. This zone was known as "customs waters" and was later called the "Contiguous Zone." By 1930 the proprietary rights of the coastal state over the resources of the territorial sea was well established, provided it did not interfere with a vessel's right of innocent passage. In 1945, President Truman issued a proclamation asserting rights to explore and exploit the oil and gas resources of the continental shelf outside of the 3 nm territorial sea. In 1953, the U.S. Congress enacted legislation over the federal and state control of the continental shelf. In 1958, international conventions were concluded in Geneva on the territorial sea, contiguous zone and continental shelf. The concept of a fishery conservation zone was born in another Truman Proclamation but Congress did not enact laws regarding a 200 nm fishery conservation zone until 1976. This evolved into a zone whereby a coastal nation had exclusive control over all economic exploration and exploitation of the natural resources off its coast. By 1982, the custom of asserting a 12 nm territorial sea, 24 nm contiguous zone, and 200 nm EEZ was codified in the United Nations Convention on the Law of the Sea (UNCLOS).

U.S. CONTROL IN MARITIME ZONES VS RIGHTS OF FOREIGN STATES

The U.S. proclaimed a 12 nm territorial sea in 1988, a 24 nm contiguous zone in 1999, and a 200 nm EEZ in 1983, consistent with customary international law as codified in UNCLOS. This customary law is a balanced compromise between a flag State's interest in maritime shipping and a coastal State's interest in protecting and managing its coastal waters. The U.S. sovereignty over its terrestrial lands extends to its internal waters and territorial sea, including the airspace above and the seabed below. Subject to ancient customs where nations should provide safe harbor to ships in danger or distress (force majure), the U.S. may restrict entry or travel through its internal waters. The U.S. may also prohibit the entry into portions of the territorial sea, provided there is still an area that allows for vessels to exercise their right of innocent passage through the territorial sea. "Passage" through the territorial sea must be continuous and expeditious, although that may include stopping and anchoring under certain circumstances. While warships are generally immune from laws and regulations, the U.S. has the right to require foreign warships comply with U.S. laws. If they don't, the U.S. may order the foreign warship to leave its territorial sea.

The contiguous zone is a buffer to the territorial sea, and within it, the U.S. may exercise the control necessary to prevent infringement of its customs, fiscal, immigration or sanitary laws and regulation of territorial sea. In addition, the U.S. may regulate the removal of cultural heritage, including foreign flagged vessels and nationals in its contiguous zone. It overlaps the EEZ which extends from the territorial sea out to 200 nm. The U.S. does not exercise sovereignty in the contiguous zone or the EEZ. It does have exclusive sovereign rights and jurisdicton for exploration and exploitation of natural resources of the seabed, subsoil, water column, and air space in the EEZ.

All of these zones have a common point of reference from which they are measured: the baseline. The rules for determining the baseline under UNCLOS are substantively the same as those under the 1958 Convention, which the U.S. ratified in 1961. As a line that marks the inner limit of the territorial sea and the outer limit of internal waters, the baseline is comprised of the low water line on NOAA charts plus closing lines across legally-defined bays and rivers. The U.S. uses a normal baseline, as opposed to a straight baseline because of its interests in preserving the freedom of navigation. One of the most important facts for those relying on NOAA's charts for the limits of these zones is that the baseline and all of the zones are ambulatory. They are subject to change due to accretion and erosion of the shore.

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