Azimuth: Horizontal direction reckoned clockwise from the meridian plane.
Contour: Imaginary line on ground, all points of which are at the same elevation above or below a specific datum.
Contour interval: Difference in elevation between two adjacent contours.
Coordinates: Linear and (or) angular quantities that designate the position of a point in relation to a given reference frame.
Datum (pl. datums): In surveying, a reference system for computing or correlating the results of surveys. There are tow principal types of datums: vertical and horizontal. A vertical datum is a level surface to which heights are referred. In the United States, the generally adopted vertical datum for leveling operations is the National Geodetic Vertical Datum of 1929. The horizontal datum is used as a reference for position. The North American Datum of 1927 is defined by the latitude and longitude of an initial point (Meade's Ranch in Kansas), the direction of a line between this point and a specified second point, and two dimensions that define the spheroid. The new North American Datum of 1983 is based on a newly defined spheroid (GRS80); it is an Earth-centered datum having no initial point or initial direction.
Elevation: Vertical distance of a point above or below a reference surface or datum.
Grid: Network of uniformly spaced parallel lines intersecting at right angles. When superimposed on a map, it usually carries the name of the projection used for the map- that is, Lambert grid, transverse Mercator grid, universal transverse Mercator grid.
Imagery: Visible representation of objects and (or) phenomena as sensed or detected by cameras, infrared and multispectral scanners, radar, and photometers. Recording may be on photographic emulsion (directly as in a camera or indirectly after being first recorded on magnetic tape as an electrical signal) or on magnetic tape for subsequent conversion and display on a cathode ray tube.
Latitude: Angular distance, in degrees, minutes, and seconds of a point north or south of the Equator.
Longitude: Angular distance, in degrees, minutes, and seconds, of a point east or west of the Greenwich meridian.
Map projection: Orderly system of lines on a plane representing a corresponding system of imaginary lines on an adopted terrestrial or celestial datum surface. Also, the mathematical concept for such a system. For maps of the Earth, a projection consists of 1) a graticule of lines representing parallels of latitude and meridians of longitude or 2) a grid.
Map series: Family of maps conforming generally to the same specifications and designed to cover an area or a country in systematic pattern.
Meridian: Great circle on the surface of the Earth passing through the geographical poles and any given point on the Earth's surface. All points on a given meridian have the same longitude.
Origin of coordinates: Point in a system of coordinates that serves as a zero point in computing the system's elements or in prescribing its use.
Prime meridian: Meridian of longitude 0 degrees, used as the origin for measurements of longitude. The meridian of Greenwich, England, is the internationally accepted prime meridian on most charts. However, local or national prime meridians are occasionally used.
Quadrangle: Four-sided area, bounded by parallels of latitude and meridians of longitude used as an area unit in mapping (dimensions are not necessarily the same in both directions). Also, a geometric figure of significance in geodetic surveying.
Scale: Relationship existing between a distance on a map, chart, or photograph and the corresponding distance on the Earth.
Survey: 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.
Topography: Configuration (relief) of the land surface; the graphic delineation or portrayal of that configuration in map form, as by contour lines; in oceanography the term is applied to a surface such as the sea bottom or surface of given characteristics within the water mass.
Universal Transverse Mercator (UTM) grid: Military grid system based on the transverse Mercator projection, applied to maps of the Earth's surface extending from the Equator to 84 Degrees north and 80 degrees south latitudes