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.
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.
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.
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.
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.
The dataset includes specific information about each maritime boundary segment. Attributes for the data are:
Boundary ID: a unique identifier of the boundary segment
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). For those seeking the ambulatory three nautical mile territorial sea limit, we recommend that you use the seamless raster nautical chart service provided by the Office of Coast Survey.
Web site owner: United States Office of Coast Survey