D

dangling strings

String (arc) that is not connected at one end to another string. This is also known as a "dead end" and indicates that topology is not complete. 

dasymetric technique

Mapping technique where symbols are used to indicate distributions, e.g., the use of dots or proportional symbols. 

data

Any information, facts, or figures (in general, programs are not considered data). In GIS, data can usually be classified as attributional, positional, or temporal. 

data acquisition

Usually refers to the automatic collection of data via sensors or measuring devices. Can also refer to the process of collecting data for subsequent entry into a computer. 

data coverage

See coverage 

data element -- database

A basic (atomic) unit of logical information in a database. In an implemented database, for each data element, there will be a "place" or "space" to store a value. 

data exchange -- alternatives

Two basic alternatives for handling data exchange: (1) standardizing on one particular system so no data conversion is necessary; (2) developing mechanisms for converting data between different systems. 

data management

Refers to all levels of managing data from computer storage and retrieval, software, standards, data administration, and organizational functions. 

data quality

In GIS, a measure or identification of how fit for use cartographic data is. Data quality applies to various levels, from an individual point to the entire data set or coverage. 

data schema

See data structure 

data set

Collection of interrelated data -- the data being organized and structured. Usually the data set is contained within a single file. 

data structure

Logical organization of data (elements, fields). Also known as data schema. 

data tablet

See digitizing tablet 

data type

Fundamental characteristic of data being stored in a computer. Common data types are: integer numeric, real numeric, character, logical (true or false), date. 

data value -- database

Refers to the information stored in a data element. 

database

Collection of related information. A GIS database includes information about the location and attributes of geographical features. 

database dictionary

Catalog or directory of information about the definition, structure, and usage of data within a database. It is meant to provide information about the data and its storage -- it does not contain any of the actual data. 

database management system (dbms)

Set of programs and utilities for organizing and manipulating the information in a database. 

database record

Collection of related, contiguous data (set of related data elements). In a GIS, this is often the attributes associated with a spatial entity. 

database structure

Refers to the overall organization of data records and elements within a database. 

datum

Properly, it is the singular for the word data. In mapping, it is the assumed horizontal surface of zero elevation. This surface forms a spheroid (defined mathematically) and is meant to approximate the shape of the earth. Survey control positions are relative to a given datum. See NAD27, NAD83 

dbms

See database management system 

DCW

See Digital Chart of the World 

decoder

Device (either hardware or software) for converting coded information back into its original form. 

defacto standard

Specification or format that is widely and commonly used but not endorsed by any official standards organization. A defacto standard through use and consensus may eventually be adopted by a standards body and become official. 

deleting -- editing function

Elimination of an element from a database. 

DEM

Digital Elevation Model. See digital terrain model 

demography

Statistical study of human populations. Term demographics refers to data collected or produced. 

derived map

Map produced (derived) from one or more other maps by analysis, modification, or combination. 

device driver

Low level routine which acts as an interface between a higher level program and an actual physical device. 

diazo process

Contact duplication process using light sensitive paper. Traditionally used to produce quick copies of single colour line maps. 

DIGEST

DIgital Geographic information Exchange STandards. Comprehensive geographic data exchange specification being promoted by DGIWG -- Digital Geographic Information Working Group. 

digital cartography

Computer assisted or aided mapping. See CAM 

Digital Chart of the World (DCW)

Meant to be a topologically based digital product of land surface information of the entire world at 1:1 000 000 scale. Is a project of the United States Defense Mapping Agency (DMA) in cooperation with Australia (DOD), Canada (DND), and the United Kingdom (MOD). When complete DCW will be distributed using CD-ROMs and will be accessible using PC-based systems. Information distributed will include cartographic, attribute, and textual data. Also included will be software needed to access and display the data. 

digital elevation model (DEM)

See digital terrain model 

digital image processing

See image processing 

digital mapping

Computer assisted or aided mapping. See CAM 

digital terrain model (DTM)

Digitally encoded information about the elevation (or variation of relief) of a given area. This gives a quantitative model of landform. Often the terms DEM (Digital Elevation Model) and DTM (Digital Terrain Model) are used interchangeably, although many prefer to use the term DEM to describe a model containing only discrete data on elevation. 

digital terrain model -- grid

DTM which describes and analyses a 3D surface by using a matrix of values with defined origin and distance between elements. A grid is one of the basic structures for processing digital elevation data. 

digital terrain model -- TIN

TIN (triangulated irregular network) is a DTM which describes and analyses a 3D surface by using a mesh of irregularly shaped (non-overlapping, adjacent) triangles. May also be referred to as TTM (Triangulated Terrain Model). 

digitize -- as an action

Conversion or encoding of coordinates or values into digital form. 

digitizing -- system mode

Digitizing may be performed in either "point mode" where each location is explicitly specified by the user, or in "stream mode" whereby locations are determined automatically based on sampling the pucks position at a predetermined rate. 

digitizing tablet/table

Flat table-like input device used to enter x,y coordinates into a computer. Usually, a piece of paper (e.g., a map) is placed flat on the table and x,y positions are indicated using a puck (or sometimes a pen shaped cursor). 

DIME

See GBF/DIME 

dimension

In municipal or roadway applications -- dimensions are the physical widths and lengths associated with parcels or constructions. 

dimensioning

Process of entering and positioning dimensions. 

dirichlet tessellation

See proximal polygons 

dissolve function

Ability to drop boundaries between adjacent polygons which possess specified attributes and form new larger polygons with new or merged attributes derived from the previous polygons. 

distance along measurement

See measurement -- distance along 

distance to measurement

See measurement -- distance to 

distributed database

Database which is physically stored in more than one computer. May be spread over a large geographic area. 

DLG

Digital Line Graph. This format was initially developed by the U.S. Geological Survey (USGS) as part of the U.S. National Mapping Program Digital Cartographic Data Standards. It was, and is, used to distribute USGS digital maps. This format is file based in structure. An enhanced version of DLG (DLG-E) is currently being developed. 

DMA

Acronym for Defense Mapping Agency in the United States. 

DMDF

Digital Map Data Format. DMDF was developed to support the Province of Alberta's 1:20,000 digital base mapping project. It was adopted and modified from the exchange format developed by G. Tychon to facilitate data exchange between the City of Edmonton and the City of Calgary. While it was designed and implemented strictly for a specific project its use expanded beyond this due to the lack of any other exchange format being readily available (at that time).

dot pitch

Refers to the width of a displayed dot on a raster display device. Often used to describe the capability of a screen or monitor (measurement is usually in millimetres -- e.g., .28 is 28/100ths of a millimetre). 

drainage model

Model to determine the drainage network from a DTM. 

draping

Display technique where planimetric information is visually overlaid on 3D perspective models (usually DTM), e.g., the display of soil polygons or a road network on a perspective display of terrain elevation. 

drop-line

Display suppression function that allows for no display of boundaries between adjacent polygons with specified attributes. This function does not involve the restructuring of coverage topology (i.e., no change to the way the actual data is stored). 

DTM

See digital terrain model 

DXF

Data eXchange Format. A CAD orientated data exchange format proposed by the manufacturers of AutoCad. 

E

ECDIS

Electronic Chart Display Information System. System used for charting and navigation. 

edge

See arc 

edge matching -- vector

As a vector function -- joining of adjacent map sheets into one map or coverage. Edge matching usually involves automatic joining of lines and polygons, and the elimination of sliver polygons (given specified tolerances). The process may also include the rebuilding of topology if performed on coverage possessing topology. Otherwise, edge matching is only a graphical merging of maps. 

EDI

Electronic Data Interchange. Exchange of information such as orders, invoices, and confirmations (at least traditionally) between organizations. 

EDIF

Electronic Design Interchange Format. Used for exchanging design information and for "design to/from foundry" communications. 

eliminate -- vector

As a vector operation -- elimination of selected polygons possessing specific spatial characteristics (e.g., area/perimeter ratio indicating sliver polygon), or attributes. 

encode

To convert data into a form which may be processed by a computer. 

end points

The two ends of a line or arc. 

entity

See spatial entity 

error types

Error types may be absolute, relative, or referential. 

exchange format(s)

Way in which data can be structured and organized to facilitate exchange between different systems. 

export

Formatting and transferring data out of a system. 

F

feature -- geographic

Generally, a real-world phenomena with spatial position, attributes, and relationships. In specific cases, it is often used to refer to a defined spatial entity and its digital (object) representation. 

feature classification

Grouping of features into predetermined classes (e.g., "primary highway" may be a feature class). The taxonomy of feature classification may be linear, hierarchical, or network in form. 

file

Collection of related data records. 

file format

Specification for the data structure of information in a file. 

file structure

Refers to both the organization of files within a system and the system defined structure or format of data within a file. 

file system

Refers to how files are organized in a computer system. 

fishnet plot

Display technique for representing 3D structures or surfaces using a deformed mesh (grid) of lines. 

flag

A flag is data which is used as an indicator (for control or command purposes). 

flagging

Marking or tagging process based on the occurrence of some specific event (e.g., search result). 

flow-line map

Map showing the movement of people, transport vehicles, etc. A line is used to indicate direction and the thickness of the line can be used to indicate quantity or volume. 

fourth generation language (4GL)

Refers to a group of high level languages used primarily for the manipulation of data bases. 4GL languages have a syntax mimicking the English language and operate on sets or subsets of data rather than on single elements as do most conventional languages (such as FORTRAN or PASCAL). 

fractal

Object which is self-similar at all scales. Regardless of scale the same level of detail and appearance is present. 

fringe

Refers to displayed areas of a map which are located outside of some specified boundaries. 

G

G

See giga 

gap -- digitizing

Refers to the distance between two digitized lines (or other digitized entities). If the entities are supposed to meet or be coincident -- the "gap" is then considered a digitizing or scanning error. 

GBF/DIME

Geographic Base File/Dual Independent Map Encoding (developed in the early 1970's by the U.S. Bureau of the Census for the storage of geographically related census information). 

generalize

Involves a reduction of detail, either by resampling to a larger cell size (as a raster operation) or reducing the number of points (as a vector operation). 

geo-spatial system

See geographic information system 

geoadministrative area

Spatially bounded area used for a specific purpose. One geoadministrative area may overlap another or be entirely within another. 

geoadministrative class

Set of geoadministrative areas sharing a common purpose. 

geocodes

Classification system and list of abbreviations used to identify and classify geographic features. May also be called feature codes. 

geocoding

Process of defining the position of geographical features relative to some reference grid. 

geodesy

Science dealing with the measurement and mathematical description of the earth -- size, shape, and gravitational field. Also refers to large scale surveys where the shape of the earth is taken into account. 

geofile

File containing geographically referenced data. 

Geographic Document Architecture (GDA)

Exchange mechanism (proposed) that organizes data into components called Content Architectures. This is similar to the concept of Office Document Architecture (ODA). GDA supposes that with many different standards for GIS interchange coming into existence and with there being little chance of convergence, some mechanism which separates content and carrier be devised. For each content type, a Content Architecture would be developed. For all Content Architectures, the same data coding and encapsulation techniques would be used. 

geographic entity

Alternate term for feature. See feature 

geographic information system (GIS)

Set of hardware, software, and procedures used to capture, manage, manipulate, analyze, model, and display spatially referenced data for problem solving/planning purposes. 

geographic projections

See Projections

geomatics

Mathematics which deal with the earth. 

Geomatics Industry Association of Canada (GIAC)

Private industry association representing businesses involved with surveying, mapping, remote sensing, and GIS in general. 

geometric transformations

Bijective mapping (one to one and onto) from the coordinate space onto itself. Major geometric transformations are scaling, translation, and rotation. 

geoprocessing

Use of computers to manipulate and analyze spatial and associated attribute data. 

georeference system

System that maps the location of points on the surface of the earth to points on a map (digital or otherwise). Universal Transverse Mercator (UTM) is an example of a georeference system. 

giga (G)

Used to indicate a billion. Is abbreviated as G. 

GIS

See geographic information system 

GIS -- application categories

Approximately a dozen broad categories comprise the bulk of GIS activities. Ranking these categories from greatest activity to lowest produces the following: Municipal activities; Utilities (various); Education -- training, and research; Forestry and forestry related; Cartography -- map production and hydrological charting; Conservation -- environmental protection and ecology; Natural resources, range management, and range resources; Agricultural -- soils and irrigation; Water resources; Demography -- medical, human, and wildlife); Roads/highways -- construction, planning, and maintenance; Market research and delivery of products. 

GIS -- data exchange standards

Currently, there are no GIS data exchange standards. Rather there are specifications that may over time, with consensus, become standards. The entire process of developing and refining GIS data exchange standards is a time consuming and complex procedure. 

GIS -- raster operation

Raster operational mode -- mode where location information is inherent in the grid (raster) data structure. 

GIS -- vector operation

Vector operational mode -- mode where x,y coordinates are use to represent locations. 

GKS

Graphical Kernel System. Device independent set of graphics primitives for creating graphics images. 

global positioning system (GPS)

Satellite based positioning system. Developed by the U.S. Department of Defense. When complete will consist of 21 satellites and will provide continuous and complete coverage of the earth. Use of radio signals from the satellites make it possible to determine the location of a GPS receiving station on the earth's surface. Depending on technology and procedures used, positioning accuracy is anywhere from a few metres to 50 metres. 

GPS

See global positioning system 

gradient

Maximum rate of change of a quantity against a horizontal distance. This value can be expressed as a ratio, decimal, percentage, or tangent of the angle of inclination. Gradient measured along a specific direction is referred to as a direction gradient. 

graphic object manipulation

Ability to manipulate on-screen elements of the display for map composition purposes. 

graphic object/entity generation

Ability to generate points describing geometrical elements such as arcs and circles from a set of parameters. 

graphical interface

See graphical user interface 

graphical user interface (GUI)

User interface which simultaneously displays pictures and images as well as text (in fact text is also treated as an image). Common examples of graphics interfaces are: Microsoft Windows, the Macintosh interface, IBM OS/2 Presentation Manager, etc. 

graphics entity

Graphics representation of a spatial entity. 

graphics primitives

Basic graphical elements used to build and draw images. These include: point or dot, line, line string, circular arc, etc. 

graphics tablet

Small digitizing tablet usually 10 to 14 inches square. 

gray scale -- graphics

Series of shades from black to white. 256 shades is usually the maximum number of shades that a scanner will produce or software packages will manipulate (256 equals 1 byte of storage). 

grid

Generally refers to a set of uniformly spaced lines intersecting at right angles to produce a pattern of rectangles (usually squares). Grids may be used to provide a reference mechanism when displaying information or to assist in the sampling of information. 

grid map

Map in which the information is displayed in the form of grid cells. 

gridded data

Data which has been sampled or calculated to a grid. 

ground survey

Survey made at ground level (as opposed to aerial surveys -- survey from above the ground). 

ground truth

Means to verify remote sensed or mathematically calculated data with actual measured field data. 

GUI

See graphical user interface