Lebanese International University
School of Engineering
Department of Surveying
Dr. Sami Makdissi
1.1 Basic definitions.
In order to gain a clear understanding of the procedures for making surveying
measurements on the earth’s surface, it is necessary to be familiar with the
meaning of certain basic terms:
1. A vertical line at any point on the earth’s surface is the line that follows the
direction of gravity at that point. It is the direction which a string will
assume if a weight is attached to the string and the string is suspended
freely at the point. At a given point there is only one vertical line.
2. A horizontal line at a point is any line that is perpendicular to the vertical
line at the point. At any point there are an unlimited number of horizontal
3. A horizontal plane at a point is the plane that is perpendicular to the
vertical line at the point. There is only one horizontal plane through a given
4. A vertical plane at a point is any plane that contains the vertical line at the
point. There is unlimited number of vertical planes at a given point.
5. A level surface is a continuous surface that is, at all points, perpendicular to
the direction of gravity. It is exemplified by the surface of a large body of
water at complete rest. For a small portion of the earth’s surface the level
surface can be regarded as a horizontal plane.
6. A horizontal distance (HD) between two given points is the distance
between the points projected onto a horizontal plane. The horizontal
plane, however, can be defined at only one point. For a survey, the
reference point may be taken as any one of the several points of the
7. A horizontal angle (HA) is an angle measured in a horizontal plane between
two vertical planes.
8. A vertical angle (VA) is an angle measured in a vertical plane. By
convention, if the angle is...