Glossary

Popular terms used throughout this website

 


ORTHORECTIFICATION

Orthorectified images are the most position-accurate products offered. The orthorectification process removes image distortions introduced by the collection geometry and the terrain, and resamples the imagery to a uniform ground sample distance and user-specified map projection.

OUTPUT MEDIA

CD-ROM and 8mm are the standard delivery media, other media types are available for a fee. Internet delivery using File Transfer Protocol (FTP) is planned for the future, but is not currently available.

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.

PAN-SHARPENED

Color images with 1-meter pixels created by merging the 1-meter Pan with the 4-meter Multispectral product of the same area.

PANCHROMATIC

This is a black-and-white image. If visual sharpness is most important, panchromatic or pan-sharpened (with color) is the best product to purchase.

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

A measurement technology in which the 3D coordinates of points on an object are determined by measurements made in two or more photographic images taken from different positions.

PHOTOMAP (Photographic Map)

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

PIXEL (derived from "picture element")

A data element having both spatial (texture) and spectral properties. The spatial (texture) variable defines the apparent size of the resolution cell (i.e., the area on the ground represented by the data values) and the spectral variable defines the intensity of the spectral response for that cell/pixel in a particular band.

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.

PLANIMETRY

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

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.