INTERSECTIONA method of locating the
horizontal position of a point by observations
from two or more points of known position, thus
measuring directions that intersect at the station
being located. A station whose horizontal position
is located by an intersection is known as an
IRRATIONAL NUMBERReal number that
cannot be expressed in the ratio of two integers;
for example, 3, n.
IRREGULAR POLYGONA nonequilateral
ISOMETRIC AXISAxis used in isometric
projections and drawings. Each line in the axis
forms an angle of 1200 with the adjacent line,
easily constructed with a straightedge and a
ISOMETRIC DRAWINGSame as an isometric
projection except that the dimensions of the object
drawn are scaled and not projected.
ISOMETRIC PROJECTIONA single view
projection of an object showing three dimensions.
The object is inclined so all faces make the same
angle with the plane of projection, making all lines
and surfaces foreshortened in the same ratio. This
allows one scale to be used throughout.
ISOSCELES TRIANGLEA triangle having two
LATERAL FACESFaces or surfaces forming
the sides of a solid figure; also known as lateral
LATERAL SURFACESSee LATERAL FACES.
LATITUDEIn plane surveying, the amount
that one end of a line is north or south of the other
end. As the plane coordinates of a point are
known as the casting and northing of the point,
the latitude is the difference between the northings
of the two ends of the line, which may be either
plus or minus. (See DEPARTURE.)
LAW OF COSINESA law of mathematics that
states that, in any triangle, the square of one side
is equal to the sum of the squares of the other
two sides minus twice the product of these two
sides multiplied by the cosine of the angle between
them. This statement may be expressed in formula
form as follows:
LAW OF SINESA law of mathematics that
states that the lengths of the sides of any triangle
are proportional to the sines of their opposite
angles. It is expressed in formula form as follows:
LAW OF TANGENTSA law of mathematics
that states that, in any triangle, the difference
between two sides is to their sum as the tangent
of half the difference of the opposite angles is to
the tangent of half their sum. For any pair of
sidesas, side a and side bthe law may be
expressed as follows:
LEADER LINESThin unbroken lines used to
connect numbers, references, or notes to
appropriate surfaces or lines.
LEGENDA description, explanation, table of
symbols, and so on, printed on a map or chart
for a better understanding and interpretation of it.
LEVEL1. Pertaining to a level surface; 2. To
make horizontal at the point of observation;
3. An instrument for leveling.
LEVEL DATUMA level surface to which
elevations are referred. The generally adopted
level datum for leveling in the United States is
mean sea level. For local surveys, an arbitrary
level datum is often adopted and defined in terms
of an assumed elevation for some physical mark
LEVEL LINE1. A line in a horizontal plane;
2. A line over which leveling operations are
LEVEL NETLines of spirit leveling connected
together to form a system of loops or circuits
extending over an area. This is also called a
vertical control net.