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b.
Nautical Charts (smaller in scale than 1:250,000)
c. Joint Operations Graphic-Ground (JOG-G) (1:250,000
scale) for islands not appearing on nautical charts smaller in
scale than 1:250,000.
d. Aeronautical Charts - only if nautical charts and
topographic maps are not available.
3.3.3 Datums of sources. The datums for all sources used
in the production of DLMB are contained in DMA TM 8358.1,
Datums, Ellipsoids, Grids and Grid Reference Systems.
3.3.4 Accuracy. Sources selected for compilation of
digital data shall have a horizontal accuracy of 518.2 meters
(1700 feet) at 90% CE (Circular Error) or better.
3.4
Datum.
3.4.1 Horizontal datum. The horizontal datum for DLMB
shall be the current World Geodetic System - 1984 (WGS 84).
3.4.2
Vertical datum.
The vertical datum shall be Mean
Sea Level.
3.5 DLMB features. There is a physical limitation to the
preciseness of digitization of features. At the scale of
1:250,000 this limitation is equal to 0.25 mm (0.01 inch) or
0.04 nautical mile (0.07 kilometer).
3.5.1
Islands.
a. Digitize all islands larger than 0.10 nautical
mile (0.18 kilometer). This is equal to 0.76 mm (0.03 inch) at
a scale of 1:250,000.
b. If a group of islands exist in a cluster and the
islands are less than 0.25 mm (0.01 inch) apart the entire group
may be encompassed and digitized as one island.
c. If an island is within 0.25 mm (0.01 inch) of a
coastal shoreline the island may be included as part of the
shoreline.
d. Rocks are digitized if they are symbolized as
islands and meet the size criterion stated for islands.
(See 3.5.1.a.)
5
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