# Grid Definitions for Land Surveyors

**grid-**^{1}A network composed of two sets of lines, each set drawn according to a definite pattern and intersecting the other in a specific geometric arrangement. The most common form of grid consists of uniformly spaced parallel lines intersecting at right angles. The term is frequently used to designate a plane-rectangular coordinate system superimposed on a map projection, in which case it generally carries the name of the projection, i.e., Lambert grid, transverse Mercator grid, Universal transverse Mercator grid. ^{2} A system of points or lines for which field measurements are made, or for which computations are made to serve as a basic control system for measuring. See also *coordinate system.*

**grid, military—**A rectangular grid; coordinate, or reference system placed on a map projection to facilitate the location and identification of map data for military purposes. The universal transverse Mercator (UTM) grid is used on maps at scales of 1:250,000 and larger between 80° North and 80° South. Beyond the 80° parallels, the universal polar stereographic (UPS) grid is used. The unit of measure is meters. These grids have been adopted by the United States and other NATO countries; however, certain exceptions are allowed for previously established grids in foreign areas.

**grid, parallactic** [PHOTOGRAMMETRY]-A uniform pattern of rectangular lines drawn or engraved on a transparent material, usually glass, and placed either over the photographs of a stereoscopic pair or in the optical system of a stereoscope to provide a continuous floating-mark system.

**grid, perspective **[PHOTOGRAMMETRY)]-A network of perspectively converging lines and their intersecting perpendicular lines drawn or superimposed by overlay on an oblique aerial photograph. The perspective grid is representative of a schematic network of coordinate grid lines on the ground or datum plane. See also *grid method, perspective *[PHOTOGRAMMETRY].

**G****rid azimuth—**At the point of observation, the angle in the plane of the projection measured between the central meridian of the plane coordinate projection system and a line containing the object sighted. Although essentially a map quantity, a grid azimuth may, by mathematical processes, be transformed into a geodetic azimuth.

**grid bearing**—See *grid azimuth; North, true.*

**g****rid cell—**A single discrete unit or square in a grid representing a portion of the Earth; for example, a square meter or square mile.

**grid** **coordinates—**See *coordinates, grid.*

**grid** **declination—**The angle, commonly denoted by ե, between the direction of grid north and geodetic north. Also called “grid convergence” or “convergence.” See also *gisement.*

**grid** **distance—**See *grid length.*

**grid** **factor—**A combination of the elevation and scale factors used to convert from ground distance to grid distance, or vice versa, in state plane coordinate systems. See *coordinate system.*

**grid length—**The distance between two points as obtained by computation from the plane-rectangular coordinates of the points. In the state plane coordinate systems, a grid length differs from a geodetic length by the amount of a correction based on the scale factor for the given line.

**grid method, perspective **[PHOTOGRAMMETRY]-A graphical method of transferring detail from oblique photographs to the plane of a map. Done by superimposing a perspective grid on the photograph for the area encompassed by the coordinate grid system of the map area. Detail is transferred by eye from interpolations on the photograph of each successive position within the perspective grid to its corresponding grid position on the map. See *grid, perspective *[PHOTOGRAMMETRY].

**grid north-**^{1}The direction of the Earth’s polar axis as plotted (or computed) on a map projection. ^{2} The angle in the plane of projection between a straight line and the central meridian (y-axis) of a plane-rectangular coordinate system.

**grid plate—**A glass plate on which an accurately ruled grid is etched. Sometimes used as a focal-plane plate to calibrate film distortion; used also for calibration of plotting instruments. Sometimes called a “reseau.”

**grid tick—**A small mark placed at the edge of a map or drawing to indicate a measurement. The grid system used may be indicated by ticks for future reference.

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

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