Terms starting with S


Relationship existing between a distance on a map, chart, or photograph and the corresponding distance on the Earth. 

SEA LEVEL (Water Level)

Height of the surface of the sea at any given time.


Unit of subdivision of a township; normally a quadrangle 1 mile square with boundaries conforming to meridians and parallels within established limits, and containing 640 acres as nearly as practicable. 


Intersection of the land with the water surface.


Mathematical figure closely approaching the geoid in form and size and used as a surface of reference for geodetic surveys. A reference spheroid or ellipsoid is a spheroid determined by revolving an ellipse about its shorter (polar) axis and used as a base for geodetic surveys of a large section of the Earth (such as the Clarke spheroid of 1866 which is used for geodetic surveys in the United States).


Point on a map or chart whose height above a specified datum is noted, usually by a dot or a small sawbuck and elevation value. Elevations are shown, on a selective basis, for road forks and intersections, grade crossings summit of hills, mountain.


Technique of distance measurement wherein the observer reads the intercept subtended on a graduated rod between two marks on the reticle of the telescope. 


A standard set of coordinate systems used in the US for mapping.


Coordinate systems established by the U.S. Coast and Geodetic Survey (now the National Ocean Survey), usually one for each state, for use in defining positions of points in terms of plane rectangular (x,y) coordinates.


Production of a map or chart manuscript from aerial photographs and geodetic control data by means of photogrammetric instruments.


Instrument for plotting a map by observation of stereomodels formed by pairs of photographs.


Imagery with three-dimensional characteristics that creates the illusion of depth.

Also, pertaining to the use of binocular vision for observation of a pair of overlapping photographs or other perspective views, giving impression of depth. 


Decrease in the elevation of land surface due to tectonic, seismic, or artificial forces, without removal of surface material. 


A near-polar orbit where the satellite always crosses the equator at the same local solar time.


Orderly process of determining data relating to any physical or chemical characteristics of the Earth. The associated data obtained in a survey. An organization engaged in making a survey.