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A-D

A

ArcInfo
- Desktop hybrid GIS software package, distributed by Environmental Systems Research Institute (ESRI). Comprised of Arc, the GIS component and Info, a relational database, although ArcInfo can also be linked to external databases such as Oracle. Unlike ArcView, ArcInfo is in a DOS environment rather than Windows and therefore has a rather steeper learning curve. A number of add-on extensions are available for example, TIN, GRID, NETWORK and COGO, which provide additional functionality.

Accessibility - An aggregate measure of how reachable locations are from a given location. Common measures of accessibility are distance and cost.

Accuracy - The closeness of observations, computations or estimates to the true value as accepted as being true. Accuracy relates to the exactness of the result, and is distinguished from precision which relates to the exactness of the operation by which the result was obtained.

Application - A process that uses data or performs some function on a computer system.

ArcView - Desktop GIS software package distributed by Environmental Systems Research Institute (ESRI). Cheaper and easier to use than ArcInfo, ArcView has become well-established as one of the world's most popular desktop mapping packages. High quality, easy to produce graphics mean that a novice user can easily manipulate high power tools. Can be linked to ArcInfo database files and can handle both vector and raster data types through the addition of extensions.

B

Base Map - A map containing visible surface features at a known level of accuracy, essential for locating or deriving additional layers, or types, of georeferenced information. (A set of topographic data displayed in map form providing a frame of reference or contextual information to the user).

C

CAD - Computer Aided Design. An automated system for the design, drafting and display of graphically oriented information.

Cadastral Map - A map showing the boundaries of the subdivisions of land for purposes of describing and recording ownership and taxation.

Cadastre / Cadastral Survey - A public register or survey that defines or re-establishes boundaries of public and/or private land for purposes of ownership and taxation.

Cartesian Coordinate System - A two dimensional coordinate system in which x measures horizontal distance and y measures vertical distance. An x,y coordinate defines every point on the plane.

CGVD28 -
Canadian Geodetic Vertical Datum 1928, mean sea level (adopted public vertical reference system.). The average height of the surface of the sea for all stages of the tide, determined by averaging height readings observed hourly over a minimum period of 19 years. (source -Survey Services 2003)

COGO -
Abbreviation for the term Coordinate GeOmetry. Land surveyors use COGO functions to enter survey data, to calculate precise locations and boundaries, to define curves, and so on.

Conversion - The process or work of transferring information from one information system to another. Conversion may be the input of data from paper maps to a computer database, or migration of data from one automated system to another.

Coverage - The Term used in the ARC/INFO GIS platform for a data theme

D

Data Format - In order for any information (including geographic information) to be usable by a computer program, it must be digitally encoded in a way the program can understand. The specific structure in which it is encoded is called a data structure, data format, or file format. In the case of vector-like geographic information, data formats include the order and style in which the coordinates representing each object are written, as well as any attributes of that object.

Data theme - A collection of one or more digital objects (whether raster or vector) that describe a particular subject matter for a given area. For example, in a municipal GIS, there might be several separate data themes, representing roads, parcels, city limits, water bodies, terrain, earthquake hazard zones, and so on. Each theme may consist of many objects representing individual geographic entities, but they are stored as a unit-either a single file or a small group of files.

DATUM - A point, line, surface or set of quantities used as a reference upon which measurements are based. (source -Survey Services 2003)

DBMS - Data Base Management System. Software that manages, manipulates and retrieves data in a database.

Digital Elevation Model (DEM) - Any data theme that digitally represents terrain (the shape of the earth's surface); the most common structures being a raster grid of elevations, and the vector triangulated irregular network (TIN).

Digital Terrian Model(DTM) - A three-dimensional model of the Earth's surface, provided in digital form.

Digital Orthophotoquad (DOQ) - A roaster data theme, built from scanned aerial photography, rectified and mosaicked to form a planimetrically correct map-like product. Used as a base for digitizing features, or as a realistic backdrop for maps.

DGI Geomatics- The academic field of study concerning the issues and fundamental concepts behind GIS. Common topics include the design of effective and efficient data structures, intuitive user interfaces, issues of accuracy, and the formal description of geographic entities, including their philosophical nature.

Drawing Exchange Format (DXF) - A vector data format developed by Autodesk. DXF is commonly used for transferring cartographic data between software platforms, but seldom used for complete GIS data transfers because it does not handle thematic attributes.

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