U.S. Maritime Limits & Boundaries Frequently Asked Questions


  1. 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)?
  2. The Bureau of Ocean Energy Management (BOEM) manages and disseminates the Submerged Lands Act federal/state boundaries. Electronic data is here. Go to the links under “GIS Data / Shapefiles” to download data for a specific region. Note: the Gulf of Mexico dataset is in the sub-link, "Gulf of Mexico Geographic Mapping Data."

  3. How are the U.S. maritime limits drawn?
  4. 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 Convention of the Law of the Sea) is the low-water line along the coast as marked on offical, 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.

    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.

  5. 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 (i.e., 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.

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

    Depending on the level of change as well as the chart production schedule (see Standing Over Notice ), the Office of Coast survey may update the digital U.S. maritime limits and boundaries as often as every few months in certain localized areas. Though we provide both dyanmic 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 updates to explain what has changed in each release of the data.

  7. 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 WMS 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.

  8. 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: ink 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.

Additional Information 
Download Maritime Limits White Paper
U.S. Maritime Zones Description in the Coast Pilot (pp. 32-34)
History of Maritime Zones under International Law
U.S. Maritime Boundary Treaties from Department of State

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