1 - NGA

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nadir polnl—See photogrepn nadir.
nadir redfsf-A radial from the nadir point.
rmdlr-polrst plot—See nedlr-polm
trlangukrtlon.
MIL-HDBK-850
nadir.point trlan@ailon-Radial lrian.
gulation in which nadir points are ulilizad as
radial centers. Also callad nedlr-pOlnt
plot.
nadir+JCS) Thet poim on the celestial
sphera directly beneath the observer and
directly opposite the zenith. See also
ground nadir; map nadir;
phOtOpFaph nadir.
nanoteala—(geomagnetiam) A unit 01
magnetic field intensity generally used in
describing the Earths megnelic field. It is
defined as 10-9 Iesla = 1 gamma. See also
gamme.
narrow-angle lens—A Ians whose total
length /s equal approximately 10 twice Ihe
diagonal of tha format.
National Geodetic Vertical datum 01
1929—Known as ‘sea level datum of
1929. prior 10 Seplembar 1973, this dalum
was established by constraining the
cumbined interconnected United States
and Canadian networks 01 Iirst-order
leveling, es it existed in 1929.
national data baae—A data base
designed, operated and maintained by any
nation for purposes specific 10 that nation.
national mao accuracv stendards—
Sasr U.S. “Nallonal Map Accuracy
Standards.
native ma~A map of any counlry
produced by that country’s governmental or
private agencies,
natural detail—The features on the Earth,
such as streams, lakes, Iorests, and
mountains; exclusive of the works 01 man.
Also called natural feature. See also
Culture; hydrographlc detail;
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hypaogrephlc datall.
natural error—Errors arising Irom variations
in temperature, humidify, wind, gravity,
refraction, and magnetic declination.
natural leature—See natural devail.
natural monument—A natural feattsra,
such as a stream, boulder, tree, etc., which
serves to mark the location of a survey “
station or land corner. Sae also
monument.
nautical broadcasta—Radio navigational
warning broadcasts to shipping on Urgent
dangers to navigation, advanced
information on changing navigational
conditions, and special warnings
disseminated by ollicial U.S. Government
proclamations alfecting shipping. This
information is also accessible on the
Navigation hflorma!ion Syslem
(NAVINFONET).
nautical chert—See hydrographlc
chart.
nautical mile—Typically, a measure of
distance equal 10 1 minute of arc 01 a great
circle. See also International Nautical
Mile.
Naval Operating Area Chart
(OP ARE A)—Naulical charw produced
and Overprinted with prescribed OPAFIEA
boundaries, submarine transit lanes,
aeronautical and olher information for fleet
exercise areas.
Naval Range Charts—Detailed
balhymelry, grid, and range boundaries;
information on range acoustics; and
seismic instrumentation.
Navigation InformalIon Network
(NAVINFONET)—The DMA data base
which contains the information to produca
the following publications: Notice to
Mariners. Summary of Corrections, Lisl of
Lighls and Fog Signals, II also provides
users access 10 upto-dale marine
information via commercial
telecommunications services.