1 - NGA

lsanomal—A line connecting polnls of equal
variations fmm a normal valua.
Ieentreplc- equal or constam entropy wl!h
respect to either space or time.
Ialande—(digital mapping) Polygons which are
completely enclosed wlthln anofher polygon.
MIL-HDBK-850
Isobaric charl-A chart showing isobars, Also
called constant pnsssura chart.
laobar—A fine alOng which the amrospheric
pressure Is, or Is assumed 10 be, the same or
constanL
lsobath—See depth contour.
Iaocenter plot—See I.eocenter
triangulation.
Isocenter triangulation—l?adial triangulation
utilizing isocenters as radial centers. Also called
}socenter plot.
Isocenier-1. (JCS) The point on a
photograph interested by the biseclor of the
angle between the plumb line and ihe
phonograph perpendicular. 2. The unique poinl
wmmon to the plane of a photograph, ita
prircipal plane, and the plane of an assumed
truly vertical phonograph taken Irom the same
camera .stafion and having an equal principal
distance. 3. The point of intersection on a
photograph of the principal line and the
isometric parallel. The isocenler Is significant
because if is the cenler of the radiation Ior
dkplacemenls 01 images due 10 lilt.
laochron~A line on a chart connecting all
points having the same lime o! occurrence of a
particular phenomencm or of a particular value
of a quantity.
laocllnal—A line drawn on a map or chart
joining points of equal magnetic dip. Also called
Isocllnlc line.
iaOCllnfC charl-A chart of which fhe chief
feature is a system 01 isocfinic lines, each for a
diiierent value of the magnetic inclinal’on.
Isocllnlc line-See Isocllnef.
isodlff-One of a series of lines on a map or
chart cvnnectfng pointa of equal correction or
dtilerence in datum, especially useful in
readjustment of suweys from one datum to
anolher. Sae also Isolat: Isolong.
Isodynamic llne-A line connecting points of
equal magnilude of any force.
laogal—A cwrtour line of equal gravhy values
on the surface of the Eatih.
lsogonal—A line drawn on a map or chart
joining points of equal magnetic declination for a
given time. Aleo celled Ieogonlc line. Sae
also agonlc IIne.
Iaogonlc chart-A chart of which lhe chief
feature is a system of isogonic Iinaa, each for a
different value of the magnetic clacllnation.
Iaogonlc llne-A tine drawn on a map or chart
iining poims of equal magnetic declination for a
given lima. The line connecting points of zero
daclinalion is the agonic tins. Lines connecfhrg
poinle of equal annual change are isopora, and
are depicfed on Magnetic Variafien charm for
the current 5-year epoch.
190gram-See Isopleth. ‘ -
Ieog rlv chart-A chart with fines connecting
points of equal grivalbn.
lsogrlv—A fine on a map or chart which joins
peinls of equal angular difference between grid
north and magnetic north.
lsolat-An isodiff connecting points ot aqual
latitude corrections.
Isollne-1. A line representing the intersection
of the plane of a vertical photograph wfth the
plane 01 an overlapping oblique phonograph. II
Ihe vertical photograph were tiff frae, the iaollne
would be fhe isomatric parallel of lhe oblique
photograph. 2. A line along which vafues are, or
are assumed 10 ba, constant.
iaolong—An isodiff corrneciing points of equal
longitude corrections.
Isomagnetic chart-A charf ahowing the
configuration of the Earth% magnetic tiefd by
isogonic, isoclinic, or isodynamic lines.
Iaometrlc (conformal) latltude—An
auxlllay latitude used in fhe mnfonnal mapping
of the spheroid on a sphere. By transfonrrirrg