Popular terms used throughout this website



A collection spatial data and related descriptive data organized for efficient storage and retirieval by many users.


A user - defined geographic phenomenon that can be modeled or represented using geographic data sets in ARC/INFO. Examples of geographic features include streets, sewer lines, Manhole cover, accidents, lot line and parcels.


An organized collection of computer hardware, software and digital geographic data designed to provide multiple layers of geographically-referenced information. GIS databases are used to efficiently capture, store, update, manipulate, analyze and display all forms of georectified information.


Figure of the Earth visualized as a mean sea level surface extended continuously through the continents. It is a theoretically continuous surface that is perpendicular at every point to the direction of gravity (the plumbline).


The photogrammetric adjustment of one or more images relative to each other and to an absolute (fixed) ground reference system. An image or vector layer that is georectified is tied to a geographic reference system such that each pixel or point chosen can be identified by geographic coordinate (latitude and longitude).


A satellite image whose geographic coordinates have been matched with known, real-world coordinates.


Pertaining to the geographic location and characteristics of natural or constructed features and boundaries on, above or below the Earth’s surface, especially when referring to data that are geographic and spatial in nature.


A satellite navigation system. A constellation of more than two dozen GPS satellites broadcasting precise timing signals by radio to electronic GPS receivers which allow them to accurately determine their location (longitude, latitude and altitude) in real time, day or night, in any weather, anywhere on Earth.


System of coordinates of latitude and longitude used to define the position of a point on the surface of the Earth with respect to the reference spheroid.


A fully intergrated grid (cell based) geoprocessing system for use with ARC/INFO. GRID supports a Map Algebra Spatial language that allows sophisticated spatial modelling and analysis.

A geographic data model representing information on an array of equally sized square cells arranged in rows and columns. Each grid cell is referenced by its geographic X, Y location.


A discreetly uniform unit that represents a portion of the Earth, such as a sq. meter or sq. mile, Each grid cell has a value that corresponds to the feature or characteristic at the site such as a soil type, census tract or vegetation class.


GCPs are accurate positions of points on the Earth's surface expressed in horizontal (latitude and longitude) and in vertical (elevation above mean sea level) measurements.


Any series of lines used on a map to indicate the general direction and steepness of slopes. The lines are short, heavy, and close together for steep slopes; longer, lighter, and more widely spaced for gentle slopes.


A picture in which the gradations of light are obtained by the relative darkness and density of tiny dots produced by photographing the subject through a fine screen. 


Maximum height reached by a rising tide. The height may be due solely to the periodic tidal forces or it may have superimposed upon it the effects of prevailing meteorological conditions. Use of the "high tide" is discouraged.

  • High Water Line: Intersection of the land with the water surface at an elevation of high water.
  • High Water Mark: Line or mark left upon tidal flats, beach, or along shore objects indicating the elevation or the intrusion of high water.