 | Glossary GIS |
A posteriori models: Models that are designed to explore an established theory.
A priori models: Models that are used to model processes for which a body of theory has yet to be established.
Aerial photograph: Photograph taken from an aerial platform (usually an aeroplane), either vertically or obliquely.
Aggregation: The process of combining smaller spatial units, and the data they contain, into larger spatial units by dissolving common boundaries and lumping the data together.
AM/FM: Automated mapping and facilities management.
Analysis scheme: The logical linking of spatial operations and procedures to solve a particular application problem.
Analytical hill shading: The process of calculating relief shadows and using these as a visualization technique to enhance the portrayal of relief on a map.
Annotation: Alphanumeric or symbolic information added to a map to improve communication.
Arc: An alternative term for a line feature formed from a connected series of points.
ARC/INFO: A leading GIS software package developed by the Environmental Systems Research Institute (ESRI).
Area: The entity type used to represent enclosed parcels of land with a common description.
Area cartogram: A type of cartogram that is used to depict the size of areas relative to their importance according to some non-spatial variable such as population or per capita income.
Artificial Intelligence (AI): Field of study concerned with producing computer programs capable of learning and processing their own thoughts''.
Artificial Neural Network (ANN): See Neural networks''.
Aspatial query: The action of questioning a GIS database on the basis of non-spatial attributes.
Aspect: The direction in which a unit of terrain faces. Aspect is usually expressed in degrees from north.
Attributes: Non-graphical descriptors relating to geographical features or entities in a GIS.
Automated cartography: See Computer cartography''.
Azimuthal projections: Map projections in which the surface of the globe is projected onto a flat plane.
Basic Spatial Unit (BSU): The smallest spatial entity to which data are encoded.
Block coding: Extension of the run-length encoding method of coding raster data structures to two dimensions by using a series of square blocks to store the data.
Boolean algebra: Operations based on logical combinations of objects (using AND, NOT, OR and XOR).
Boolean overlay: A type of map overlay based on Boolean algebra.
Buffering: The creation of a zone of equal width around a point, line or area feature
Canadian Geographic Information System (CGIS): An early GIS using data collected for the Land Inventory System that was developed as a result of the requirements of the Canadian Agriculture and Development Act.
Cartesian co-ordinates: The system for locating a point by reference to its distance from axes intersecting at right angles, often represented as a grid on a map.
Cartograms: Maps that show the location of objects relative to a non-Euclidean variable such as population density or relative distance.
Cartographic modelling: A generic methodology for structuring a GIS analysis scheme.
Cartography: The profession of map drawing; the study of maps.
CASE tools: Computer-assisted software engineering. Software tools used to help reduce program development time.
CD-ROM: Method of storing large volumes of data on optical discs.
Census: The collection of data about the entire population of a country or region.
Central point linear cartogram: A form of cartogram that shows space distorted from a central point on the basis of time taken or cost incurred to travel to a series of destination areas.
Chain coding: Method of raster data reduction that works by defining the boundary of the entity.
Chaos theory: Idea that seemingly minor events accumulate to have complex and massive effects on dynamic natural systems.
Chart junk: Unnecessary, often confusing, annotation added to maps and charts.
Choice alternatives: Range of feasible solutions to be evaluated in a decision problem in MCE.
Choice set: The set of choice alternatives in MCE.
Choropleth map: A thematic map that displays a quantitative attribute using ordinal classes. Areas are shaded according to their value and a range of shading classes.
Cleaning: See Data editing''.
Computer-aided cartography: See Computer cartography''.
Computer-aided design (CAD): Software designed to assist in the process of designing and drafting. This is normally used for architectural and engineering applications, but can also be used for drafting maps as an input to GIS.
Computer-assisted cartography (CAC): Software designed to assist in the process of designing and drawing maps.
Computer-assisted drafting (CAD): See Computer-aided design (CAD)''.
Computer cartography: The generation, storage and editing of maps using a computer.
Computer movies: Animated maps showing how a chosen variable changes with time. These are used to spot temporal patterns in spatial data.
Conceptual data model: A model, usually expressed in verbal or graphical form, that attempts to describe in words or pictures quantitative and qualitative interactions between real-world features.
Concordancediscordance analysis: Method of MCE based on lengthy pairwise comparison of outranking and dominance relationships between each choice alternative in the choice set.
Conic projections: Map projections in which the surface of the globe is projected onto a cone (for example, Alber''s Equal Area projection).
Constraints: Set of minimum requirements for a decision problem in MCE.
Contour: A line on a topographic map connecting points of equal height and used to represent the shape of the Earth''s surface.
Cookie cutting: See IDENTITY overlay''.
CORINE: The Co-ordinated Information on the European Environment programme, initiated in 1985 by the European Union to create a database that would encourage the collection and co-ordination of consistent information to aid European Community policy.
Criteria: Attributes by which choice alternatives are evaluated in MCE.
Cylindrical projections: Map projections in which the surface of the globe is projected onto a cylinder (for example, the Mercator projection).
Dangling arc: A dead-end line or arc feature that is connected to other lines in the data layer at one end only.
Data: Observations made from monitoring the real world. Data are collected as facts or evidence, which may be processed to give them meaning and turn them into information.
Data accuracy: The extent to which an estimated data value approaches its true value.
Data bias: The systematic variation of data from reality.
Data conversion: The process of converting data from one format to another. With the many different GIS data formats available this can be a difficult task requiring specialized software.
Data editing: The process of correcting errors in data input into a GIS. This can be carried out manually or automatically.
Data error: The physical difference between the real world and a GIS facsimile.
Data input: The process of converting data into a form that can be used by a GIS.
Data precision: The recorded level of detail of the data.
Data stream: The process of progressing from raw data to integrated GIS database. This includes all stages of data input, transformation, re-projection, editing and manipulation.
Database: A collection of data, usually stored as single or multiple files, associated with a single general category.
Database management system (DBMS): A set of computer programs for organizing information at the core of which will be a database.
Decision support system (DSS): A system, usually computerized, dedicated to supporting decisions regarding a specific problem or set of problems.
Delaunay triangulation: Method of constructing a TIN model such that three points form the corners of a Delaunay triangle only when the circle that passes through them contains no other points.
Deterministic model: A model for which there is only one possible answer for a given set of inputs.
Differential GPS: The process of using two GPS receivers to obtain highly accurate and precise position fixes.
Diffusion: The spatio-temporal process concerned with the movement of objects from one area to another through time. Examples include forest fire development, the movement of pollutants through any medium, and the spread of a disease through a population.
Digital elevation model (DEM): A digital model of height (elevation or altitude) represented as regularly or irregularly spaced point height values.
Digital mapping: See Computer cartography''.
Digital terrain model (DTM): A digital model of a topographic surface using information on height, slope, aspect, breaks in slope and other topographic features.
Digitizer: A piece of computer hardware used to convert analogue data into digital format. See Digitizing table'', Scanner'' and Laser line follower''.
Digitizing: The process of converting data from analogue to digital format.
Digitizing table: A table underlain by a fine mesh of wires and connected to a computer that allows the user to record the location of features on a map using an electronic cursor. These are used to digitize maps and other graphical analogue data sources manually.
Disaggregation: The reverse of aggregation''.
Distance decay: A function that represents the way that some entity or its influence decays with distance from its geographical location.
DouglasPeucker algorithm: A geometric algorithm used to thin out the number of points needed to represent the overall shape of a line feature.
DXF: Data eXchange Format. A file format used for the exchange of GIS data.
Dynamic model: A model in which time is the key variable whilst all other input variables remain constant. Outputs from the model vary as time progresses
