GIS is also generally considered as a specific subset of the overall field. According to Understanding GIS (ESRI, Redlands, Calif.) a true GIS system can be used to perform each of the following five functions:

The GIS can answer what exists at a specific location. The location can be described using place name, ZIP code, latitude and longitude or other location systems.

The GIS can find locations satisfying specified conditions (e.g. an undeveloped parcel of land zoned for light industrial, at least 10 acres in size, with railroad access).

The GIS can spot changes in an area over a certain period of time.

The GIS can find patterns. For example, it could test the hypothesis that proximity to PCB-laden transformers is a factor in the incidence of cancer in children.

The GIS could model various scenarios. For example, if 10 inches of rain fell in a certain watershed, where would flooding occur and at what hour.

GPS coordinates

Global Positioning System coordinates -- a system of locating points on or above the earth through triangulation of satellite signals.

Ground Control Points

Point on the surface of the earth with known coordinates as represented by some geographic grid reference system.


Property of colors ranging from red, yellow, green and blue, determined by the dominant wavelength of light emitted or reflected from the surface.


Camera systems able to record many spectral wavelength bands (up to several hundred) extending from ultraviolet to visible, beyond infrared.


The intensity of light per unit area of its source.


Camera systems sensitive to more than one spectral wavelength band.

One-Meter Ground Pixel Resolution

The smallest feature that can be discerned (in one pixel) is one meter in length or width.


Corrected or "straight" images. When images are made of large areas of the earth, they are skewed by the angle of the earth to the camera, the curvature of the earth, surface irregularities, etc. Orthoimages are corrected to remove such effects.


Correcting an image (see "Orthoimages" above).


Fineness of detail that can be distinguished in an image, as on a video display terminal. "Display Resolution" is the density of the pixels that compose an image. "Spatial Resolution" is the smallest possible map feature that can be accurately displayed at a specified map scale.


Vividness or intensity of hue.

USGS Quad Maps

Maps produced by the United States Geological Survey showing one quadrangle, or one atlas sheet.


URISA GIS Glossary

Understanding GIS, ESRI, Redlands, CA

The American Heritage Dictionary of the English Language

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