| Graphical version | Site Map |
| MAGIC |
Glossary
Select a letter below to find a word. If a word is not listed and you would like a definition, please contact us.
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
AGI
ASSOCIATION FOR GEOGRAPHIC INFORMATION A UK multi-disciplinary non-governmental
organisation dedicated to the advancement of the use of geographically related
information. Its mission is to spread the benefits of GIS throughout the community
and to help all users and vendors of GIS.
ALPHANUMERIC
A term which describes any letters, numbers, and punctuation marks treated as
characters. It is not the same as 'numeric', which refers to numbers that have
a value and can be used in mathematical calculations. The term is also used
as an adjective to describe items, such as keyboards, which allow these characters
to be entered into a computer in readable code.
APPLICATION
A practical use of computer software, systems or concepts.
BASE MAP
A map containing geographic features used for locational reference. Roads, for
example, are commonly found on base maps.
BINARY
A base 2 number that uses only the data values of 0 or 1. It is the fundamental
basis of all digital computing.
BIT
An abbreviated term for binary digit, and the smallest unit of computer data.
BITMAP
An unstructured grid image in which data values are recorded as either 1 or
0. The term is often used to refer to graphics composed of pixels, for example,
scanned maps or photographs.
BOUNDARY
A continuous line which delineates the edge of a polygon or study area.
BUFFER
1) A region of a specified width around a point, line, or area. it is a type
of proximity analysis that is supported by most GIS and is defined in such systems
by real-world distances from one or more map elements. 2) A temporary storage
area held in computer memory or on disk.
BYTE
A unit of computer storage of BINARY data usually comprising eight BITS, and
equivalent to a character. Computer memory and storage is measured in this unit,
giving rise to terms such as Kilobyte (approximately one thousand bytes), Megabyte
(approximately one million bytes) and Gigabyte (approximately one thousand million
bytes).
CGM
COMPUTER GRAPHICS METAFILE A standard file format specification (ISO 8632) for
the storage and transfer of graphic information.
CLASS
A set of ENTITIES possessing certain common ATTRIBUTE VALUES.
CLASSIFICATION
The grouping of ENTITIES into a set of CLASSES according to certain common ATTRIBUTABLE
VALUES.
CO-ORDINATE
x, y and possible z-values defining a position in terms of a spatial reference
framework.
CO-ORDINATE POINT
A location in space defined by measured linear or angular positions within a
SPATIAL REFERENCE system. In a 2D Cartesian CO-ORDINATE SYSTEM this location
is often designated as (x, y).
CO-ORDINATE SYSTEM
A fixed reference framework superimposed onto the surface of an area to designate
the position of a point within it. The CARTESIAN CO-ORDINATE system and the
system of latitude and longitude used on the Earth's surface are common examples.
CONTOUR
A line connecting points of equal surface value.
CURSOR
A pointer or other symbol on a screen that indicates the active position. Movement
of the cursor is generally accomplished through the use of a mouse or other
pointing device.
DATA
A collection of facts, concepts or instructions in a formalised manner suitable
for communication or processing by human beings or by automatic means. In GIS
applications they are often observations or measurements of the natural or human
environment.
DATA CAPTURE
The processing of converting data into digital form by DIGITISING, scanning,
or direct recording of real-world phenomena.
DATA CLASSIFICATION
The division of a set of data or ENTITIES into subsets such that entitles within
each subset share some common features.
DATA COLLECTION
The process of collecting data by survey for conversion to digital form. This
includes aerial and satellite surveys, ground surveys, and census surveys.
DATA CONVERSION
The conversion of data from an original form (paper or electronic) into a form
suitable for a particular use in a digital form compatible with the computer
system, software, and other data being used.
DATA FORMAT
A specification which defines how data is structured in a file and which determines
such aspects as the sequence of data items, their length, and necessary HEADER
data.
DATA INPUT
The entry of information into a computer. This may be accomplished through the
use of a keyboard, DIGITISER, SCANNER, or from already existing data sets.
DATA ITEM
A sequence of related characters which can be defined as the smallest logical
unit of data that can be independently and meaningfully processed. For example,
this might be an x, y CO-ORDINATE pair of values.
DATA QUALITY
An assessment of the completeness, currency, logical consistency, and accuracy
of data for a particular purpose.
DATA SET
An organised collection of data with a common theme.
DATA STRUCTURE
A logical arrangement of data used by a specific computer system for data management,
storage, and retrieval. It includes a reference linkage system between data
items.
DATA TRANSFER
The movement of data from one computer system or software to another. It often
requires a change of DATA FORMAT.
DATABASE
A logical collection of interrelated information, managed and stored as a unit,
usually on some form of mass-storage system such as magnetic tape or disk. A
GIS database includes data about the spatial location and shape of geographic
features recorded as points, lines, areas, pixels, grid cells, or tins, as well
as their attributes.
DATABASE MANAGEMENT SYSTEM
DBMS A collection of software for organising the information in a database.
Typically it contains routines for data input, verification, storage, retrieval,
and combination.
DATUM
1) Any point, line, or surface used as a reference for a measurement of another
quantity. 2) A model of the Earth used for geodetic calculations.
DOTS PER INCH
DPI A unit of measurement expressing the resolution of scanners, monitors, or
printing devices. The greater the number of dots per inch, the more detail may
be captured or displayed by the device.
EDIT
The process of adding, deleting, and changing data.
ELECTORAL WARD
The fundamental spatial unit used in the division of voting areas in the UK.
ENTITY
A general term for a real-world thing or digital phenomenon. A house, a road
segment, and an ELECTORAL WARD are all examples.
ENTITY CLASS
A specified group of real-world things, for example, a road network.
ENTITY RELATIONSHIP MODEL
A logical way of describing real-world things and their relationships - a necessary
first step during database design. This leads to the development of a conceptual
model of the relationships between the elements which will be contained within
the database and ensures an efficient database design. Also known as an ER model.
ERROR
In GIS, errors may be associated with mistakes in either the spatial or ATTRIBUTE
VALUES of the data. These may result from the original state of the data, from
data input methods, of from functions and algorithms applied in the GIS.
ERROR PROPAGATION
The compounding of errors in computational results during data analysis. Such
error propagation is brought about by errors in the data, by poorly designed
algorithms, or by low numeric precision.
EXTRAPOLATION
A method or technique to extend data or inferences beyond known values.
FEATURE
A group of spatial elements which together represent a real-world entity. Often
used synonymously with the term object. A complex feature is made up of more
than one group of spatial elements, for example, a set of line elements with
the common theme of roads representing a road network.
FEATURE CODE
An ALPHANUMERIC code which identifies, describes, and/or classifies a set of
spatial elements.
FIELD
1) A set of ALPHANUMERIC characters comprising a unit of information. 2) A location
in a data record in which a unit of information is stored. For example, in a
database of addresses, one field would be 'city'.
FILE
A named set of computer records stored or processed as a unit.
FILE FORMAT
A structure for organising data in a computer file. May be unique to a specific
computer programme or may conform to a general standard.
FONT
A design type of ALPHANUMERIC characters and symbols. Some of the most commonly
used are Helvetica, Times Roman, and Courier.
FORMAT
A systematic and repeatable arrangement of computer data.
GEOCODE
A code associated with a spatial element which describes its location. For example,
this might be a co-ordinate or a postcode.
GEOCODING
The process by which the geographic co-ordinates of a location are determined
by its address, postcode, or other explicitly non-geographic descriptor.
GEOGRAPHIC DATA
Any information which includes a description of a location on or near the Earth's
surface. This may include generic descriptions, for example, place names or
particular geological strata.
GEOGRAPHIC INFORMATION SYSTEM
See GIS.
GEOMETRY
In GIS, an ambiguous term often used to describe the manner in which a real-world
ENTITY is represented geometrically in a database. Thus, the shape of an entity
could be described in terms of its stored co-ordinates and the lines between
these co-ordinates. For example, the geometry of a highway systems might be
described as a network or a set of lines and intersections or nodes.
GEOREFERENCE SYSTEM
A CO-ORDINATE SYSTEM for points on the Earth's surface. Examples of such a system
are the Universal Transverse Mercator system (UTM) and the latitude and longitude
graticule.
GIS
GEOGRAPHIC INFORMATION SYSTEM. An organized collection of computer hardware,
software, geographic data, and personnel designed to efficiently capture, store,
update, manipulate, analyze, and display all forms of geographically referenced
information.
GREY SCALE
A range of intensities between black and white through shades of grey.
GRID REFERENCE
The position of a point on a map expressed in terms of co-ordinates of a planar
CO-ORDINATE SYSTEM. Some countries, for example, France, New Zealand and the
UK, have developed their own National Grid which is a system used to reference
points within them.
GUI
GRAPHICAL USER INTERFACE An interface between the computer and the person using
it, which makes use of icons, menus, and a pointing device to select options
and to execute commands or graphs. It usually has the capability to display
more than one WINDOW on the same screen.
HARD COPY
A print or plot of output data on paper or film media.
HARD DISK
A large capacity mechanical, magnetic computer storage device for programmes
and data. Generally installed internally in a computer and non-removable although
external removable versions are available.
HARDWARE
The various physical components of an information processing system. The term
refers to devices such as the computer, the screen, plotters, and printers.
HEADER
The initial lines in some data files which contain information on the data present
(see METADATA). This might include the number of records and columns and the
numerical format of the data.
HIGHLIGHTING
A means of emphasising a display element by modifying its visual attributes.
ICON
A graphic symbol, displayed on a screen, that the user can point to with a device,
such as a mouse, in order to select a particular function or software application.
IMPORT
The process of bringing data or programs from one computer system into another.
INTERACTIVE
Describes the two-way communication between the computer and the user in which
responses from one are immediately relayed to the other, either through the
keyboard or by display on the screen.
INTERNET
An international network of dispersed local and regional computer networks used
predominantly for sharing information and resources. Developed primarily for
military and then academic use, it is now accessible through commercial on-line
services to the general public.
INTERSECTION
The point at which one line crosses another. In GIS there are a number of contexts
in which this is used, for example, in polygon overlay analysis to create the
intersection of two area features. Intersection of two lines.
ISO
INTERNATIONAL STANDARDS ORGANISATION A world-wide federation of national standards
bodies that defines rules, criteria, or measurements that are to be adopted
as international standards.
KEY
A unique identifier for each RECORD in a table or each ENTITY in a data set
which is used to link this table or data set to others. See also RELATIONAL
JOIN.
LABEL
An ALPHANUMERIC element, used with the VECTOR DATA MODEL, that displays attribute
values or identifiers for points, lines, or polygons.
LAND COVER
The surface materials, such as crops and water, that are found in an area.
LAND PARCEL
A unit of land, usually delineated according to land ownership or land use.
LASER PRINTER
An output device which user laser technology, similar to that used in photocopiers,
to print text and images onto paper.
LATITUDE
The angular distance north or south between a point on the Earth's surface and
the Equator. The distance is measured with reference to an idealised, spheroid-shape
of the Earth.
LAYER
A usable subdivision of a data set, generally containing elements of a particular
theme. The subdivisions are registered to a common CO-ORDINATE SYSTEM, thus
enabling analysis and integration across the various themes.
LEGEND
A part of a map which contains explanation of the symbols, colours, and shading
that have been used to code the various elements and data values.
LICENCE
In common GIS usage, licence refers to the legal agreement between a software
company and the user which determines how that software may be used. Licences
generally limit the number of computers on which a single software package can
be used.
LINE
1. A set of ordered coordinates that represents the shape of geographic features
too narrow to be displayed as an area at the given scale (e.g., contours, street
centerlines, or streams), or linear features with no area (e.g., state and county
boundary lines). 2. A single arc in a coverage. 3. A line on a map (e.g., a
neatline).
LINEAR FEATURE
A geographic feature that can be represented by a line or set of lines. For
example, rivers, roads within a pizza delivery area, and electric and telecommunication
networks are all linear features. Linear features are represented in ARC/INFO
by arcs or by the route-system feature class.
LONGITUDE
The angular distance of a point east or west of an arbitrarily defined meridian,
usually taken to be the Greenwich meridian. The distance is measured with reference
to an idealised, spheroid shape of the Earth.
LOOKUP TABLE
A table which contains a key field and related values which can be linked to
other data tables to provide additional ATTRIBUTE VALUES about the ENTITIES.
MAINTENANCE
In common GIS usage, maintenance refers to the full suite of operations which
is required to keep a database and/or a commercial software product current.
Software maintenance generally involves a contract between the software vendor
and the user for which the user pays an annual fee.
MAP
A graphic representation of geographically distributed phenomena. The information
displayed may be in the form of symbols or signs. Accuracy and detail are functions
of map projection and scale.
MAP SCALE
See SCALE.
MENU
A list of options displayed by a data processing system, from which the user
can select an action to be initiated. These choices may be displayed in the
form of ALPHANUMERIC text or ICONS.
MENU BAR
An area along one edge of a window within a computer package used to display
names or icons for a menu.
METADATA
Information about data. Examples are data quality information, currency, LINEAGE,
ownership, and feature classification information.
MOUSE
A hand-operated device used for pointing at and selecting areas on a computer
screen. The location of the pointer on the screen is manipulated by moving the
mouse over another screen.
MULTI-MEDIA
A combination of several communication media such as still and moving pictures,
sound, graphics, and text.
NATIONAL GRID
See GRID REFERENCE.
NETWORK
1) A geometric or logical arrangement of nodes and interconnecting lines. 2)
A database structure in which the links and relations between various data are
explicitly defined. 3) A group of linked computers which are able to share software,
data, and various hardware devices such as printers.
NODE
An intersection point where two or more arcs or lines meet.
NULL VALUE
The absence of a value. If a particular column of a row in a table is null,
that means there is no value stored. Null is not the same as blank or zero.
OBJECT
In recent years this has taken on a more specific usage with reference to GIS.
It is a digital representation of a discrete spatial entity. An object may belong
to an object class and will thus have ATTRIBUTE VALUES in common with other
defined elements.
OBJECT CLASS
A set of objects with a specific theme such as 'stream' or 'woodland'. A hierarchical
approach may be adopted in defining these sets, and ATTRIBUTE VALUES may be
inherited from levels above a particular class.
OBJECT ORIENTATION
A method of organising data, commands, operations, and real-world elements whereby
they are encapsulated into various discrete objects. This term has been applied
to databases, programming languages, and recently to GIS.
ORIGIN
The reference point (0,0) from which co-ordinates are measured.
PACKAGE
A set of computer programs that can be used for a particular generalised class
of APPLICATION.
PAN
To move the viewing window up, down, or sideways to display areas in a geographic
data set which, at the current viewing scale, lie outside the viewing window.
See also zoom.
PARCEL
See LAND PARCEL.
PIXEL
1) The smallest element of a display device, such as a video monitor, that can
be independently assigned attribute, such as colour and intensity. 2) In remote
sensing, refers to the fundamental unit of data collection. A pixel is represented
in a remotely sensed image as a rectangular cell in an array of data values.
The term is an abbreviation for 'picture element'. A pixel within a grid cell
arrangement.
POINT
A single x,y coordinate that represents a geographic feature too small to be
displayed as a line or area; for example, the location of a mountain peak or
a building location on a small-scale map.
POLYGON
An area bounded by a closed line. It is used to describe spatial elements, such
as housing and industrial units, administrative and political districts, and
areas of homogeneous land use and soil types.
POP-UP WINDOW
A WINDOW that appears on the display surface in response to some action.
POSTCODE
A coding system for referencing all properties in a country which have a postal
address. The term is used generally, except in the US where the more specific
term zipcode is used. The UK, for example, is divided into 120 areas, each area
is divided into districts, each district into sectors, each sector into units.
A unit postcode applies to a group of addresses of (approximately 15) neighbouring
properties. It does not define an area.
PULL-DOWN MENU
A list of functions or commands that appears below the menu bar when the user
selects a name or ICON from it.
RDBMS
RELATIONAL DATABASE MANAGEMENT SYSTEM A database management system that organises
data into a series of records held in linked tables. It allows different relations
between the various records, fields, and tables to be established and is used
to aid in data access and transformation.
RECORD
A set of related data fields describing a single ENTITY which is grouped as
a unit for processing. For example, in an address database, the fields which
together provide the address for a specific individual comprise a record.
RESOLUTION
A measure of the ability to detect variation. High resolution implies a high
degree of discrimination but has no implication as to accuracy. See also SPATIAL
RESOLUTION.
SCALE
The ratio or fraction between the distance on a map, chart, or photograph and
the corresponding distance in the real world.
SCALE BAR
A map element which shows the scale graphically.
SOFTWARE
The programs, procedures, rules, and their associated documentation, for a computer
system.
SPATIAL DATA
Any type of data which includes a formal locational reference such as a grid
reference. This includes remotely sensed as well as map data. See also GEOGRAPHIC
DATA.
SPATIAL QUERY
A query which selects features based on their location or geographic relationship
to others.
SPATIAL REFERENCE
A co-ordinate, textual description or codified name by which an ENTITY can be
related to a specific position or location in space.
SPATIAL RESOLUTION
A measure of the smallest area identifiable on an image as a discrete separate
unit. In raster data, it is often expressed as the size of the raster cell.
In remote sensing, it is defined in terms of the diameter of the ground area
that may be distinguished and is often comparable to the size of the earth's
surface covered by a single pixel. The remote sensing systems on board the METEOSAT
series of satellites have a spatial resolution of approximately 900m whilst
those on the SPOT series can resolve features down to 10m size.
SQL
STRUCTURED QUERY LANGUAGE A standard language used with relational database
products which enables the user to build complex logical expressions identifying
the data to be recalled and manipulated.
STRING
A sequence of line segments or text items. It does not have topological properties.
SYMBOL
A graphic representation of a concept that has meaning in a specific context.
It is used in cartography to show the presence of ENTITIES such as churches,
post offices, and public houses.
TABLE
A means of organising data in rows and columns in which each row represents
an individual entity, record, or feature and each column represents a single
FIELD or attribute value.
THEMATIC MAP
A map depicting one or more specific topics or subjects. Examples include land
classification, population density, and rainfall maps.
THEME
A user-defined perspective on a coverage, grid, tin or image geographic data
set specified, if applicable, by a coverage name and feature class or data set
name, attributes of interest, a data classification scheme, and theme-specific
symbology for drawing.
THRESHOLDING
A technique of data transformation which compares the values of an input data
set to a specific given value, the threshold. A new data set will be constructed
in which input values are converted to one of three output values, indicating
whether the input value was over, equal to, or below the threshold.
TRANSFER FORMAT
A format for transferring digital data between computer systems and software.
In general usage this can refer not only to the organisation of data, but also
to the associated information, such as attribute codes, which is required in
order to complete the transfer successfully.
UPDATE
1) The process of adding to or revising existing data to take account of change.
2) A revision to a software product offering improved functionality and bug
fixes.
WINDOW
1) A part of a display image with defined boundaries in which information, images,
or commands are displayed and through which the user is able to interface with
the computer. In many computer systems it is possible to have several windows
open at the same time in order to see different views of the data or to control
different parts of the program simultaneously.
WYSIWYG
WHAT-YOU-SEE-IS-WHAT-YOU-GET A capability to display information on a screen
exactly as it will be printed or plotted on an output device.
ZOOM
The capability for progressive scaling of the entire display image to give the
visual impression of movement of display elements towards or away from the observer.
A zoom operation changes the scale at which an image is being displayed.
|
Online Resources
|
Help
|
About MAGIC
|
| DirectGov | Invest to Save |