national geodetic vertical datum of 1929
Reference surface established by the U.S. Coast and Geodetic Survey in 1929 as the datum to which relief features and elevation data are referenced in the conterminous United States; formerly called "mean sea level 1929."

National Map Accuracy Standards
Specifications promulgated by the U.S. Office of Management and Budget to govern accuracy of topographic and other maps produced by Federal Agencies.


navigable waters
Water usable, with or without improvements, as routes for commerce in the customary means of travel on water.

neatline
Line separating the body of a map from the map margin. On a standard quadrangle map, the neatlines are the meridians and parallels delimiting the quadrangle.

oceanic survey
Survey or examination of condition in the ocean or any part of it, with reference to animal or plant life, chemical elements present, temperature gradients, etc. See: hydrographic survey

offshore
Comparatively flat zone of variable width that extends from the outer margin of the rather steeply sloping shoreface to the edge of the continental shelf.

orientation
Establishing correct relationship in direction with reference to points of the compass; the state of being in correct relationship in direction with reference to the points of the compass.

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.

orthophotograph
Photograph having the properties of an orthographic projection. It is derived from a conventional perspective photograph by simple or differential rectification so that image displacements caused by camera tilt and terrain relief are removed.

orthophotographic map
Map produced by assembling orthophotographs at a specified uniform scale in a map format.

orthophotomap
Orthophotographic map with contours and cartographic treatment, presented in a standard format, and related to standard reference systems.

orthophotoquad
Monocolor orthophotgraphic map presented in a standard quadrangle format and related to standard reference systems. It has no contours and little or cartographic treatment.

orthophotoscope
Photomechanical device used in conjunction with a double-projection stereoplotter for producing orthophotograph.

overedge
Any portion of a map lying outside the nominal map border (neatline).

overlay
Printing or drawing on a transparent or translucent medium intended to be placed in register on a map or other graphic and which shows details not appearing or requiring special emphasis on the base material.

overprint
New material printed on a map or chart to show data of importance or special use, in addition to those data originally printed.


parallel of latitude
A circle, or approximation of a circle, on the surface of the Earth, parallel tot he Equator, and connecting points of equal latitude; a circle of the celestial sphere parallel to the ecliptic, and connecting points of equal celestial latitude.

photogrammetry
Science or art of obtaining reliable measurements or information from photographs or other sensing systems.

photomap (photographic map)
Map made by adding marginal information, descriptive data, and a reference system to a photograph or assembly of photographs.

plain
Region of uniform general slope, comparatively level, of considerable extent, and not broken by marked elevations and depressions (it may be an extensive valley floor or a plateau summit); an extent of level or nearly level land; a flat, gently sloping, or nearly level region of the sea floor.

planetable
Instrument consisting essentially of a drawing board on a tripod and some type of sighting device (alidade) with attached straightedge, used for plotting the lines of survey directly from observation in the field.

planimetric map
See: map, planimetric

planimetry
Plan details of a map - those having no indication of relief or contour.

plat
Diagram drawn to scale showing all essential data pertaining to the boundaries and subdivisions of a tract of land, as determined by survey or protraction. As used by the Bureau of Land Management, the drawing which represents the particular area included in a survey, such as township, private land claim, or mineral claim, and the lines surveyed, established, or retraced, showing the direction and length of each such line; The relation to the adjoining official surveys; the boundaries, descriptions, and area of each parcel of land subdivided; and, as nearly as may be practicable, a representation of the relief and improvements within the limits of the survey.

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.

projection, map
See: map, projection

public land system
Public lands are subdivided by a rectangular system of surveys established and regulated by the Bureau of Land Management. The standard format for subdivision is by townshipsmeasuring 6 miles (480 chains) on a side. Townships are further subdivided into 36 numbered sections of 1 square mile (640 acres) each.

quad-centered photograph
Middle exposure of a phototriplet (three consecutive aerial photographs) take so that the middle photograph is exposed directly above the center of the quadrangle and the preceding and following photographs are exposed directly above the boundaries of the quadrangle. The flying height is set such that the quad-centered photograph covers the entire quadrangle.

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.