# Plane Definitions for Land Surveyors

**plane**—Surface without curvature, such that a straight line joining any two of its points lies wholly within the surface.

**plane, horizontal-**^{1} A plane perpendicular to the direction of gravity; and plane tangent to the geoid or parallel to such a plane. ^{2} In land surveying, a plane perpendicular to the plumb line within which or on which angles and distances are observed. For any planimetric survey it is assumed that all plumb lines therein are parallel, and all horizontal planes therein are parallel.

**plane, perspective**—Any plane containing the perspective center. Because the intersection of two planes is a straight line, it follows that the intersection of a perspective plane with the ground will always appear as a straight line on a photograph. it also follows that any straight line in the object space will appear as a straight line on the photograph.

**plane, vertical**–^{1} Any plane passing through a point on the Earth and containing the zenith and nadir of that point; also a plane containing a plumb line. ^{2} A plane at right angles to a horizontal plane within which angles and distances are observed.

**plane angle**—See *angle.*

**plane coordinates**—See *coordinates, state plane; coordinate system: coordinates, **grid.*

**plane rectangular coordinates**—See *coordinates, plane rectangular*

**plane surveying**—See *surveying, plane.*

**planetable (surveying)**—A device for plotting survey data directly from field observation. A planetable consists of a drawing board on a tripod with a sighting instrument, generally a telescopic alidade, to measure and plot angles graphically.

**planetable traverse**—See *traverse, planetable.*

**planimeter**—A mechanical integrator for measuring the area of a plane surface. See also *planimeter, polar.*

**planimeter, polar**—An instrument used in measuring areas from a drawing. the instrument rotates about a pole, hence its name.

**planimetric map**—See *map, planimetric.*

**Planimetry-**^{1} The science of measuring plane surfaces; horizontal measurements. ^{2} Parts of a map which represent everything except relief; that is, works of man, and natural features such as woods and water.

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Source: NSPS “Definitions of Surveying and Related Terms“, used with permission.

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