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U.S. Marine Cadastre - Seabed and Subsoil Boundaries
U.S. Baseline Points • State
Seaward Boundary • Offshore Lease Blocks
• Revenue Sharing Boundary
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| Description: Baseline points from which the Submerged Lands
Act boundary is measured. |
| Primary Agency: Minerals Management Service (MMS). |
| Spatial extent: "Ordinary low water," interpreted
as mean lower low water, as depicted on National Ocean Service nautical
charts and/or appropriate supplemental information (Thormahlen 1999b). |
| Description: Submerged Lands Act, sec. 1312. U.S. Code
43 U.S.C. §§ 1301 et seq. (UNCLOS 1997), art. 16(1). |
| Official Depiction: MMS official protraction diagrams,
leasing map, and supplemental official outer continental shelf block
diagrams. |
| Known Digital Data Source: The following MMS website is http://www.mms.gov/ld/maps.htm |
| Notes: Baseline points are ambulatory unless "fixed"
under a joint motion by the U.S. Supreme Court (e.g., parts of Florida).
Baseline points are fixed for Submerged Lands Act purposes only. |
| Issues: Incomplete for some areas (e.g., southwest Florida).
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| Description: The limit of the state's jurisdictions under
the Submerged Lands Act (SLA). Although many exceptions exist, the
land and resources between the ordinary high water mark and the
state seaward boundary (SSB) are generally held in trust by the
coastal state for the benefit of the public (CSO 1997). |
| Primary Agency: Minerals Management Service (MMS). |
| Spatial extent: Three nautical miles (although it is three
marine leagues, or nine nautical miles, for Texas and for the Gulf
coast of Florida, and Puerto Rico) measured from the Submerged Lands
Act baseline. |
| Description: Submerged Lands Act, sec. 1312. U.S. Code
43 (U.S.C. §§ 1301 et seq.) also, 30 CFR 256.8. |
| Official Depiction: May appear on some National Oceanic
and Atmospheric Administration (NOAA) nautical charts as the Natural
Resource Boundary. |
| Known Digital Data Source: The following MMS website is
http://www.mms.gov/ld/maps.htm |
| Original Metadata: Available from MMS. |
| Notes: Federal land ownership and mineral resource management
are supported within the SSB. The boundary is ambulatory unless
"fixed" under a joint motion by the U.S. Supreme Court
(Thormahlen, 1999b). |
| Issues: Offshore boundary lines are measured along an arc
over the earth's ellipsoidal surface (chord length); therefore,
arc distance varies with latitude and azimuth corresponding to variations
in the radius of the earth's surface. As a result, the arc length
must be computed (in three-dimensional space) separately for each
stretch of coastline, even though the projection distance remains
unchanged (Ball 1997). Many boundaries have been created using a
buffer function in a geographic information system. This process
does not take into account chord length or distortion due to projection
and often may result in an inaccurate representation of the "envelope
of arcs." Accordingly, the GIS boundary data may not accurately
reflect the official or actual boundary. |
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| Description: An offshore cadastre that defines approved
subdivisions of the outer continental shelf (OCS) within federal
jurisdiction. |
| Primary Agency: Minerals Management Service (MMS) |
| Spatial extent: Dependent on the official protraction diagram
by Minerals Management Service. Generally, the spatial extent is
bounded and limited by the state seaward boundary, exclusive economic
zone (EEZ) limit, and international maritime boundaries. |
| Description: Submerged Lands Act (30 C.F.R. 256.8b). |
| Official Depiction: Official Minerals Management Service
protraction diagram. |
| Unofficial Digital Data Source: The following MMS website is http://www.mms.gov/ld/maps.htm |
| Notes: Developed and maintained by MMS. These blocks legally
define areas on the continental shelf in support of the federal
offshore leasing program. |
| Issues: Possible conversion accuracy issues because data
maintained in State Plane Coordinate System. Also, some MMS
regions are still using North American Datum 1927 horizontal
datum. |
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| Description: Provided for states to claim an equitable
share of revenues when a federal lease is within three miles of
the territorial sea boundary. The amendments mandate that 27 percent
of all revenues from production within three miles seaward of the
federal/state boundary is to be given to the states. |
| Primary Agency: Minerals Management Service (MMS). |
| Spatial extent: State Seaward Boundary (SSB) plus three
nautical miles. |
| Description: Outer Continental Shelf Lands Act. (U.S. Code
43 U.S.C. § 1337(g)). |
| Official Depiction: MMS official protraction diagram. and
supplemental official outer continental shelf block diagram. |
| Known Digital Data Source: The following MMS website is
http://www.mms.gov/ld/maps.htm |
| Original Metadata: Available from the MMS. |
| Notes: Although this boundary is complete for the Southeast
Atlantic U.S., certain geographic areas are not completed. |
| Issues: Metadata and spatial data inconsistencies exist.
Offshore boundary lines are measured along an arc over the earth's
ellipsoidal surface (chord length); therefore, arc distance varies
with latitude and azimuth corresponding to variations in the radius
of the earth's surface. As a result, the arc length must be computed
(in three-dimensional space) separately for each stretch of coastline,
even though the projection distance remains unchanged (Ball 1997).
Many boundaries have been created using a buffer function in a geographic
information system. This process does not take into account chord
length or distortion due to projection and often may result in an
inaccurate representation of the "envelope of arcs." Accordingly,
the GIS boundary data may not accurately reflect the official or
actual boundary.
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