 | Glossary for students E-L |
Ecological fallacy: A problem associated with the modifiable areal unit problem'' that occurs when it is inferred that data for areas under study can be applied to individuals in those areas.
Edge matching: The process of joining data digitized from adjacent map sheets to ensure a seamless join.
Electronic distance metering (EDM): A theodolite combined with an optical rangefinder for accurate distance measurements.
Enumeration district (ED): The area over which one census enumerator delivers and collects census forms. The size of these units, though small, is enough to ensure anonymity of census respondents in data reported at this level of detail.
Envelope polygon: The external polygon of a vector map inside which all other features are contained.
Epsilon modelling: A method of estimating the effects of positional error in GIS overlay operations. Epsilon modelling is based on the use of buffer zones to account for digitizing error around point, line and area features.
Equilibrium forecast model: A model in which forecasts are made on the basis of change in one or more elements of the system or process whilst all other factors remain constant.
Error propagation: The generation of errors in a GIS database at various stages of the data stream and during subsequent analyses.
Euclidean distance: A straight-line distance measured as a function of Euclidean geometric space.
Evaluation matrix: A matrix containing criterion scores (rows) for each choice alternative (columns) in the choice set for any MCE problem.
Evapotranspiration: The process by which water vapour re-enters the atmosphere directly through evaporation and from plant transpiration.
Eyeballing: See Line threading''
Feasibility study: An evaluation of the costs and benefits of adopting an IT solution to a problem.
Feature codes: Unique codes describing the feature to which they are attached in the GIS database.
Features: See Spatial entities''.
Filter: A cell matrix of varying shape and size used to modify the cell values in a raster map layer through a variety of mathematical procedures such as mean, sum, maximum and minimum. A filter is often used to smooth noisy data.
GANTT charts: Graphical time charts used to assist project management.
Gazetteer: A dictionary or index of geographical names.
General systems theory: A theory based on the idea that to understand the complexity of the real world, we must attempt to model this complexity.
Generalization: The process by which information is selectively removed from a map in order to simplify pattern without distortion of overall content.
Geographical analysis: Any form of analysis using geographical data.
Geomorphology: The study of the Earth''s surface and the physical processes acting on it.
Global Positioning System (GPS): A system of orbiting satellites used for navigational purposes and capable of giving highly accurate geographic co-ordinates using hand-held receivers.
GLONASS: Global Orbiting Navigation Satellite System. The Russian equivalent of the US GPS system.
Graphical User Interface (GUI): Computer interface, such as MS Windows, that is used to provide a user-friendly interface between a user and the computer.
Great circle: A circle with the same diameter as the Earth. This is used to describe the shortest route between any two points on the Earth''s surface.
Groundwater percolation: The process by which water from the soil enters the underlying geology by slow downward movement.
Hard systems analysis: A set of theory and methods for modelling the complexity of the real world.
Hydrological cycle: A dynamic natural system concerned with the circulation of water through the atmosphere, biosphere and geosphere.
Ideal point analysis: An MCE algorithm based on the evaluation of choice alternatives against a hypothetical ideal solution.
IDENTITY overlay: Polygon-on-polygon overlay corresponding to the Boolean OR and AND overlays. The output map will contain all those polygons from the first map layer and those which fall within these from the second map layer. Also referred to as cookie cutting''.
Infiltration rate: The rate at which surface runoff and precipitation soaks into the ground surface.
Internet, The: The global network of computers, originally set up as a means of secure communications for military and intelligence purposes.
Internet protocols: An established language used for the communication between systems on the Internet. HTTP and TCP/IP are examples.
INTERSECT overlay: Polygon-on-polygon overlay corresponding to the Boolean AND overlay. The output map will contain only those polygons that cover areas common to both sets of input polygons.
Intranet: A secure closed network that uses Internet protocols.
Isoline: A line joining areas of equal value.
JAVA Applet: A program that will run within a web page, written in the JAVA language.
Landsat: An orbiting satellite giving regular repeat coverage of the whole of the Earth''s surface.
Laser line follower: An automatic digitizer that uses a laser beam to follow and digitize lines on a map.
Latitude: Angular measurement north and south of the equator. Represented on the globe as parallel lines circling the globe perpendicular to the lines of longitude.
Layer-based approach: An approach to organizing spatial data into thematic map layers, wherein each map layer contains information about a particular subject and is stored as a separate file (or series of files) for ease of management and use.
Line: Entity type used to represent linear features using an ordered set of ( x , y ) co-ordinate points or a chain of grid cells.
Line-in-polygon overlay: The process of overlaying a line map over a polygon map to determine which lines cross which polygons.
Line of true scale: Line on a map along which distances are not distorted due to the effects of the map projection method used.
Line threading: A method of spatial interpolation reliant on estimating isolines through a series of observed values by hand and eye.
Lineage: The record of a data set''s origin and all the operations carried out on it.
Linear weighted summation: The simplest MCE algorithm based on the simple addition of weighted criterion scores for each alternative. Under this decision rule the choice alternative with the maximum score is the best.
Link impedance: The cost associated with traversing a network link, stopping, turning or visiting a centre.
Linked display: Method of dynamically linking map and non-map output such as charts and data plots such that changes in one are reflected by changes in the other. Such displays are used to aid exploratory data analysis.
Local area network (LAN): A local network of computers, usually within the same building, which may be used, for instance, to connect a GIS fileserver to a number of GIS access terminals.
Location-allocation modelling: The use of network analysis to allocate the location of resources through the modelling of supply and demand through a network.
Longitude: Angular measurement east and west of the prime or Greenwich meridian. Represented on the globe as a series of great circles intersecting at both poles.
Loose coupling: A method of linking models to GIS in which the user may have to perform transformations on the data output from GIS, spatial analysis or process modelling software before they can be used in another software environment.
