HACHURESA method of portraying relief by
short, wedge-shaped marks radiating from high
elevations and following the direction of slope to
HALF SECTIONA sectional view that passes
halfway through the object; used when the shape
of one half is identical to the other half.
HATCHINGSections lines that are drawn on
the internal surface of sectional views; may be
used to define the kind or type of material of
which the sectioned surface consists.
HEIGHT OF INSTRUMENT1. (Spirit
leveling) The height of the line of sight of a
leveling instrument above the adopted datum.
2. (Stadia surveying) The height of the center of
the telescope (horizontal axis) of transit or
telescopic alidade above the ground or station
mark. 3. (Trigonometrical leveling) The height of
the center of the theodolite (horizontal axis) above
the ground or station mark.
HELIOTROPEAn instrument composed of
one or more plane mirrors so mounted at the
station being sighted upon that the suns rays can
be reflected to any one observing the station.
HEPTAGONA polygon of seven sides.
HEXAGONA polygon of six sides.
HIDDEN LINESThick, short, dashed lines
indicating the hidden features of an object being
HORIZONTAL ANGLEThe angle formed by
two intersecting lines on a horizontal plane.
HORIZONTAL CONTROLControl that
determines horizontal positions only, with respect
to parallels and meridians or to other lines of
HORIZONTAL DATUMIn plane surveying,
the grid system of reference used for the
horizontal control of an area; defined by the
casting and northing of one station in the area,
and the azimuth from this selected station to an
HORIZONTAL DIRECTIONA direction in a
HORIZONTAL DISTANCEA distance
measured along a level line. It is commonly
thought of as the distance between two plumb
lines. The distance may be measured either
horizontally or inclined, but the inclined distance
is always reduced to its horizontal length.
HORIZONTAL LINEA line tangent to a level
surface, or a line lying on a horizontal plane.
HORIZONTAL PLANEA plane perpendicular
to the direction of gravity.
HORIZONTAL POSITIONThe grid position
of a horizontal control point.
HORIZONTAL REFRACTIONA natural
error in surveying that is the result of the
horizontal bending of light rays between a target
and an observing instrument. This refraction is
usually caused by the differences in density of the
air along the path of the light rays, resulting from
HORN CENTERDevice used to prevent the
compass needle from making holes in a drawing.
HUBA wooden stake or pipe set in the ground
with a tack or other marker to indicate the exact
position. A guard stake protects and identifies the
HYDROSCOPIC MOISTUREThe films of
adsorbed moisture that may be present in airdried
soil. Hydroscopic moisture may be driven off by
oven-drying. (See also adsorbed moisture.)
ILLUSTRATION BOARDSmooth white paper
with a cardboard backing, used for signs or charts
or mounting of maps, photos, or drawings that
require a strong backing.
IMAGE PLANESee PLANE OF PROJEC-
INDIA INKDrawing ink consisting of a
pigment (usually powdered carbon) suspended in
an ammonia-water solution.
INFINITE DISTANCEAn indefinite unmea-
surable distance; for example, parallel lines are
said to converge at infinity.
INSCRIBED FIGUREA figure that is
completely enclosed by another figure.