# Elevation Definitions for Land Surveyors

elevation—The vertical distance from a datum, generally mean sea level, to a point or object on the earth’s surface. The terms “elevation” and “altitude” are sometimes used synonymously, but in modern surveying practice the term “elevation” is preferred to indicate heights on the Earth’s surface, whereas “altitude” is used to indicate the heights of points in space above the ellipsoid representing the sea level surface of the Earth.

elevation, adjusted– The elevation resulting from the application of an adjustment correction to an orthmetric adjustment correction to an orthometric elevation. Also, the elevation resulting from the application of both an orthometric correction and an adjustment correction to an orthometric elevation. Also, the elevation resulting from the application of both an orthometric correction and an adjustment correction to a preliminary elevation.

elevation, field– An elevation obtained from computations using measurements of elevation made in the field (on the ground).

elevation, spot– A point on a map or chart whose height above a specified reference datum is noted, usually by a dot or a small sawbuck and elevation value; spot height.  Elevations are shown, wherever practicable, for road forks and intersections, grade crossings, summits of hills for road forks and intersections, grade crossings, summits of hills, mountains and mountain passes, water surfaces of lakes and ponds, stream forks, bottom elevations in depressions, and large flat areas.

elevation, standard– An adjusted elevation based  on the Sea Level Datum of 1929 (now known as the National Geodetic Vertical Datum of 1929) or some other definite epoch.  In some localities, this is modified by a regional adjustment, e.g., the Pacific Northwest Supplemental Adjustment.

elevation datum– See datum, elevation

elevation factor– The ratio of the radius of the earth (R) to the sum of the radius of the earth, a line’s average orthometric height (H), and the geoidal separation (N).  A line’s ellipsoidal length can be calculated by multiplying the line’s horizontal distance and it’s elevation factor.  This is acceptable for use in local surveys due to the relatively short distances involved.

elevation meter– A mechanical or electromechanical device on wheels that measures slope and distance, and automatically and continuously integrates their product into difference of elevation.

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

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