Resource Library: Graphics/graphics-16000.iso/msdos/mapping/ozgis80/ozgis18.tut

Text File | 1992-01-04 | 40KB | 494 lines

                        GLOSSARY OF TERMS
                       =================

The purpose of this tutorial is to provide definitions for a number of
terms used within this Guide.  Most of these terms are commonly used words
or phrases which have taken on a more precise technical meaning in one of
the areas spanned by the OzGIS system.  Technical terms have been
borrowed from the jargon of statistics, data processing, computer software
and hardware, cartography, and graphic arts.  Because of the diversity of
these disciplines, it is unlikely that a potential OzGIS user will have
developed a level of expertise in each.  This glossary should provide most
of the information necessary for communicating the basic concepts of
OzGIS.

The glossary is available on-line, and is accessed by typing 'G' to a menu
selection request.

Area - 1) A measurement of the size of a geographical region whose shape is
   displayed on the OzGIS monitor.  2) An arbitrary portion of the face
   of the monitor.

Attribute - A general term for the variable associated with a set of
   geographic zones, lines or sites to be processed by OzGIS.
   Attributes may be variates, statistics or simply data collected for each
   item.  Note that the modes of display for an attribute are usually
   referred to as "single variate" or "bi-variate".  See also Variate and
   Statistic.

Background - The informationless area displayed on the monitor around a map
   and its associated components.  Usually given a user selected, neutral
   colour such as black or white.

Bit - A unit of information representing the value (either 1 or 0) of a
   single binary digit.

Bivariate - A display of the relative distribution of two different sets
   of statistics on the same map.  It must be noted that no relationship
   between the two statistics is implied by the display.  For example, if
   the distribution of little old ladies is displayed simultaneously with
   the distribution of cricket players, the result is not a display of the
   distribution of little old ladies who play cricket.  See also Variate.

Boundary - A set of lines displayed on the monitor to represent the edges
   of polygons defined to the system.  Often the same as zone edges.

Byte - A group of eight bits.  See also Bit.

Catchment - The region of influence around a site e.g. suburbs around a
   shopping centre where most of the customers live.


Character - A single symbolic pattern which may be displayed on either the
   monitor or terminal.  It may be alphabetic, numeric, or punctuational,
   as the normal symbols encountered on a typical typewriter keyboard, or a
   special symbol generated for display as an entity, such as a square root
   symbol.

Choropleth Map - A map portraying the values of an attribute averaged over
   data collection units (or zones) and represented by a symbol covering
   the entire unit.  A map displayed by OzGIS represents the zones by a
   uniform colour.

Class - A convenient subdivision of the total range of values of a
   particular statistical variate.  Classes are usually chosen to make
   computations or analyses less labourious, or to make the results of such
   analyses more obvious or meaningful.  For example, the range of a set of
   values might be divided into ten equal classes in order to highlight
   items in the top ten percent.  See also Variate, Class Boundary, Class
   Interval and Class Number.

Class Boundary - The special values of variates which determine the upper
   and lower limits of the range of a class.  See also Class.

Class Interval - The range of variate values between the upper and lower
   limits of the class.  See also Class.

Class Number - A cardinal number assigned to each class into which a
   particular statistical range has been divided.  Conventionally, the
   class whose members have the lowest magnitude is assigned number 1, with
   class numbers increasing uniformly as the magnitude of class values
   increases.  See also Class.

Colour - One of the combinations of blue, green, and red which may be
   specified for display on the monitor.  The total number of colours
   available depends on the display system.

Colour Space - The range of colours which may be specified for display on
   the colour monitor.  Since the colours are specified as values of blue,
   green, and red, it is convenient to think of the colour space as a cube
   located on a standard three dimensional coordinate system.  Black is
   placed at the origin, with each of the x, y and z axes representing
   blue, green, and red, respectively.  The range of possible values is 0.0
   to 1.0 on each axis of the cube.

Continuous Colour - A method of representating statistical values
   associated with map zones by graduating zone colours to correspond with
   changes in statistical value.  From a user defined, or default, sequence
   of colours, OzGIS generates the intermediate colours to provide a
   12 colour graduated path through the colour space.  The statistic to be
   represented is quantized into 12 equal value classes, and the classes
   are assigned colours from the generated colour sequence.  This allows
   small changes in statistical value to be represented by subtle changes
   in colour, while large changes in value may be visually observed as
   significant colour differences.


Controller - A general term applied to a piece of intermediate equipment in
   the data path between the electrical signals of a processor and their
   physical realization in a peripheral device.  Within OzGIS, the term
   will most often be used for the Color Display Controller.
   It will be used to a lesser extent to describe interface controllers for
   the various disc and tape drives.

Coordinate - One of a pair of numbers which designates the location of a
   geographic point with respect to another known point.  Geographic files
   for entry into the system under OzGIS must have their points
   specified in appropriately scaled and formatted coordinates.  The
   coordinates specified by the user are converted by OzGIS for display
   on the monitor.  On the monitor screen, the origin is in the lower left
   hand corner of the viewing area.  The coordinates of a point on the
   monitor screen are specified by their distance right and up from the
   origin

Crosshair Cursor - A pair of lines at right angles to each other which is
   displayed on the monitor to designate the location of a certain point of
   interest.  Under most circumstances, the location of the crosshair
   cursor may be controlled by movements of the mouse.  See also Box
   Cursor, and Joystick.

Data - Numerical values associated with certain physical phenomena, such as
   128 cm long, 14 years old, or 43 kangaroos.  As a generality,
   OzGIS was not designed to handle data, but rather the statistics
   derived from data, such as average length, medium age, or number of
   kangaroos per hectare.  See also Statistics.

Decile - One of the nine data values which divide the range of a variate
   into ten equal sized classes.  See also Quantile and Percentile.

Default - A set of parameters automatically selected by OzGIS in the
   absence of any stated preference by the user.  The actual default
   parameters may be defined by the user in the users default file.  For
   example, OzGIS may initially display a map by arbitrarily selecting
   zone colours from a palette of possible shades which the user selected
   previously.  After this default colouring, the user may wish to change
   some particular zone colour to improve the appearance of the display.

Disc - An electronic device for storing digital data on a rotating plate
   coated with magnetic material.  See also Controller.

Display - As a verb, the act of presenting information on the monitor or
   terminal for the purpose of visually communicating that information to
   the user.  This includes all the procedures necessary to correctly
   present the information in a format suitable for both the equipment and
   the viewer.  Example:  "A map is displayed on the monitor, while a menu
   is displayed on the terminal".


   As a noun, the presentation which is visually perceived when a user
   looks at the screen of the monitor or terminal;  the total information
   content on the screen.  Examples:  "The terminal display indicates the
   options possible now";  "This map display is too red".  See also Monitor
   and Terminal.

Display Elements - The components or items of a display on the OzGIS
   monitor;  for example, legend, title, image map, boundaries, image
   symbols, histograms.

Distribution - The manner in which a number of samples of data are spread
   across the range of possible values.  May be a subjective statement,
   such as:  "These data appear to have an even distribution".  More often,
   some quantifiable measure will be given such as:  "These data have a
   normal distribution with a mean of 40 and standard deviation of 3".
   Sometimes, distribution information will be presented in graphical form,
   such as a histogram or scatter diagram.

Equal Value Quantization - A method of dividing the range of values of a
   statistical variate into a number of classes where the magnitude of the
   range of each class is the same.  See also Class.

Excluded Zone - A zone displayed on the map and coloured with a special
   shade indicating that it has not been used for quantization or has been
   omitted from the area of interest.

File - A number of data items grouped together and considered as a unit for
   convenience of storage and retrieval by a computer.  Within OzGIS,
   such files are stored as distinct entities on disk.  Files are
   identified by media designation, name, and type.  The OzGIS user
   normally supplies only the file name, but the storage media may also be
   specified.  The file type is supplied by the system.  The same name may
   be used for files of different types, but within a particular type, no
   two files may have the same name.

Frequency - A statistical term referring to the number of members of a
   population falling into a specified class.  See also Class.

Geographic Data - Digitized map data which are referenced to a geographic
   (or spatial) coordinate system, usually a map projection.

Graphics - Data which can be displayed on the monitor in terms of lines
   points and text, as opposed to colouring and filling regions of the
   screen.  Used to refer to geographic and symbol data.

Histogram - A type of bar graph in which vertical rectangles are erected on
   the horizontal axis with the height of each bar representing the
   frequency, and the width representing the corresponding class interval,
   for each of the classes of a particular variate.  OzGIS can display
   such statistical information on the monitor.  See also Scatter Diagram,
   and Class.


Information - The subjective knowledge which may be associated with an
   objective set of data.  The ages and locations of children are data;
   the distribution of school age children is statistic;  where the schools
   should be built is information.  See also Data and Statistics.

Interval - The numerical distance between the upper and lower limits of a
   class.

Joystick - An electro-mechanical device which converts the positions of a
   small lever into electrical voltages.  The voltages are further
   converted into digital signals which are used by the PDP11 to
   position various cursor patterns on the monitor screen.  See also Box
   Cursor, and Crosshair Cursor.

Legend - A display on the monitor which indicates the correspondence
   between the statistical values and their associated colours or symbols
   as defined for a particular map.  The legend usually occupies
   approximately the rightmost one fifth of the viewing area of the monitor
   and has two general forms, single variate and bivariate.  One type of
   single variate legend consists of a column of coloured rectangles beside
   which are numbers indicating the corresponding class boundaries for
   those colours.  The other is a rectangular column with colours gradually
   changing from top to bottom, and an upper and lower number indicating
   the range across which the "Continous Colour" varies.  The bivariate
   legend consists of a 45 degree parallelogram divided left to right and
   up and down into coloured smaller parallelograms.  A set of numbers
   along the left side indicates the class boundaries of the primary
   variate, while similar numbers across the upper side indicate the
   secondary variate class boundaries.

Line - This term has three special meanings within OzGIS in addition to
   its normal English usage.  (1) Any set of contiguous segments comprising
   the section of a zone boundary which has one zone on its right and a
   second zone on its left as part of a map.  (2) Any contiguous set of
   segments as part of a graphics display.  (3) A set of alpha-numeric
   characters meant to be displayed as one row on either the monitor or the
   terminal.

Location - The position of a datum point, or pixel, on the monitor screen.
   This is given by its x and y coordinates, with the origin in the lower
   left hand corner.  The range of values depends on the display system.

Lookup Table (LUT) - A table in the display system which can modify the
   value in memory for display purposes.

Map - Geographic data which can be displayed on the monitor by colouring
   and filling regions of the screen or as lines or symbols.

Map Projection - Refers to the coordinate system used for processing the
   display of a map.


Markers - Special characters or symbols which may be displayed on the
   monitor to identify locations of points.  For example, aircraft
   symbols to indicate the location of airports.  Different sized markers
   are used to show the classification of site attribute data.

Mean - The arithmetic average of a set of data values.

Memory - A portion of the OzGIS hardware used for the storage of data
   by the altering of the electrical state of the appropriate circuitry.

Menu - An itemized list of alternative actions which might be selected
   within OzGIS.  Menus are displayed on the terminal.  The terminal
   keyboard is used to enter selections from the options listed on the
   menu.  The sequence of menu items which is selected controls the "flow"
   of the OzGIS program through its various tasks.

Monitor - The electronic equipment, resembling a colour television
   receiver, on which maps and graphics are displayed.

Nested Means - A quantization method in which classes are generated by
   dividing each variate range into two classes about the mean for that
   range.  For example, the central class limit is set at the overall mean,
   then the upper and lower classes are each divided at the means of the
   two parts, giving four classes.  This process may be repeated, giving
   eight classes.

Operating System - Computer software provided to facilitate usage of the
   various computer resources available within the OzGIS system.

Overlay - As a noun, overlay refers to graphic data written on top of the
   existing display.  This is displayed on the monitor as though placed
   between the previous display and the viewer.  Overlays generally are
   entered in the refresh memory in single bit planes.
   As a verb, overlay refers to the act of adding graphics data to a
   display by putting it "on top of" the previous display.

Palette - An array of coloured rectangles which is displayed on the monitor
   at certain stages of OzGIS.  The palette shows a range of colours
   which are available for selection by the user.  Palettes are held as
   files within OzGIS.  Several palette files are provided as part of
   the software package.

Parameter - A general term referring to a physical characteristic which may
   be measured or quantified in some way, even though the precise value of
   that measurement may be unknown in specific instances.  For example, age
   is a parameter of human beings.

Percentile - One of the set of 99 values which divide the range of a
   statistic into 100 equal sized classes.

Peripherals - Items of auxillary equipment added to a computer to enhance
   its performance.  These include such items as disc drives, tape drives,
   and printers.


Pixel - The smallest, individually controllable, element (or cell)
   displayed as dots of colour on the monitor's screen.  The monitor area
   is made up of lines of pixels.  For each pixel, there is a corresponding
   location in the refresh memory for storing the data value associated
   with that pixel.  This location is the smallest datum area which can be
   individually controlled by the software.  See also Image and Location.

Point - A geographic feature which, for display purposes, may be described
   by only indicating its location as an x and y coordinate.

Polygon - A geographic area described by the line segments forming its
   boundary and the zone name which forms its surface.  One or more
   polygons may be combined to form a zone.

Presentation Maps - A set of maps prepared for rapid display on the
   monitor.

Primary Variate - The set of statistical values characterized by a common
   name which is displayed on any given single variate map.  Two such sets
   of values are displayed on a bivariate map.  The primary variate is
   named at the top of the title, and its colour values are indicated in
   the rows of the legend.  See also Variate.

Processor - The hardware which executes the procedural and computational
   tasks specified by OzGIS.  The standard OzGIS processor is a
   Digital Equipment Corporation minicomputer, the VAX.

 Projection - The representation of a physical shape on the screen of the
   monitor according to a fixed mathematical coordinate system.  Normally,
   a projection in OzGIS terms will refer to a method for presenting
   maps of geographic areas.  See also Map Projection.

Quantile - Any of the specific values which divide the range of a statistic
   into equal sized classes.  Some values have other special terms, i.e.,
   if the range is divided into four classes, the boundary values are
   called quartiles.  See also Percentile.

Quantify - To assign a number or quantity to an otherwise unnumbered
   entity.  In particular, to assign a class number to a statistical value
   or zone name.

Quantization - The process of assigning class numbers to zones according to
   the value of the statistic for that zone.  Viewed the other way,
   quantization is the process of putting zones into classes.

Quartile - One of the three data values which divide the range of a variate
   into four equal sized classes.  See also Quantile and Percentile.

Raster - a term applied to image data.  In particular data handled on a
   line basis.


Refresh Memory - The portion of the hardware (within the display
   controller) which holds the digital data necessary to continuously
   regenerate the colour monitor display.  The cathode ray tube (CRT) of
   the monitor produces its display by electrically stimulating various
   phosphorus based compounds deposited on its face.  The colours thus
   produced fade rapidly with time and must be continually "refreshed".
   The data necessary to perform this refresh correctly is stored in the
   refresh memory.

Region - A designated portion of a map displayed on the monitor.  A region
   consists of one or more zones or parts of zones defined in some way
   (e.g. a circular region centered at a point on the map).  The concept of
   a region is important when the displayed map consists of several
   geographic areas.  In this context, a region consists of a window
   (geographic area) and its displayed viewport on the screen (screen
   area).  See also Area.

Save - To store on disc (or magnetic tape) all the pertinent data regarding
   a map displayed on the monitor.  The maps which are "saved" can later be
   fully regenerated with all details preserved.

Scatter Diagram - A two dimensional plot of points whose x and y
   coordinates are the values of the individual variates associated with
   those points.  Scatter diagrams are displayed on the monitor in
   conjunction with bivariate maps.  In this instance, each map zone is
   assigned a point on the diagram.  The y-coordinate of the point
   corresponds to the value of the primary variate for that zone as
   displayed on the map.  The x-coordinate of the point has a similar
   relationship to the secondary variate.  In addition, the point will be
   coloured the same as its associated map zone.  Scatter diagrams provide
   a visual method of assessing the correlation between the two variates
   displayed on the map.

Secondary Variate - The second set of statistical values which are
   displayed (along with a primary variate) on the map.  The
   secondary variate is named at the bottom of the title.  See also Primary
   Variate.

Segment - A set of connected straight lines defined to OzGIS by
   specifying the coordinates of their starting, intermediate, and end
   points, along with the names of the two zones on either side of the
   lines.  Consequently, segments must represent a portion, or all, of the
   boundary between two zones.  See also Line and Boundary.

Site - A geographic location that has associated attribute data.  A site is
   defined by a name and fixed location e.g. a site could be a city or a
   retail store.

Standard Deviation - A statistical measure of the dispersion amongst a set
   of measured values.  The standard deviation is mathematically equivalent
   to the positive square root of the variance of the sample on which the
   statistic is based.


Statistics - A general term referring to:  1) The branch of mathematics
   involved with performing certain analytical calculations regarding
   various relationships among sets of numerical data, and 2) The numerical
   results of such calculations.  The height of an individual is data;  the
   average height of a group is a statistic.

Status - The present condition of the software and hardware system,
   especially as to its progress toward the completion of the tasks at
   hand.  The status messages are displayed as a response to
   typing interpretation of various abbreviated messages displayed on the
   terminal.  The status messages are displayed as a response to typing an
   "S" command.

Terminal - An item of hardware comprising a keyboard for entering commands
   to the processor, and some means for the processor to return
   alpha-numeric messages to the user.  The standard OzGIS terminal is
   the Digital Equipment Corporation VT100.  This contains the necessary
   keyboard, and a cathode ray tube for displaying processor generated
   messages.  Some OzGIS installations may also have a printer terminal
   for providing a permanent copy of the messages on paper.

Territory - a zone which has been formed by amalgamating bas zones e.g. sales
   territories formed from postcodes.

Text - Combinations of characters which may be specified by typing at the
   terminal.  Lines of text may be displayed on either the terminal or the
   monitor in various fonts.  See also Character, and Line.

Time Lapse Maps - A formatted set of maps concerning a geographic area and
   certain statistics associated with it as they have been collected over
   time.  Time lapse files are used to display the time related changes in
   the statistical data by rapid and periodic changes in map colours
   corresponding to the statistics.  For example, variations in population
   density, as recorded by the 1971, 1976, and 1981 census data, could be
   shown by changing the colours of the displayed map at one second
   intervals corresponding to the 3 sets of data.

User - The person who is interactively controlling the OzGIS system at
   the terminal.

Value - The number associated with a particular statistical item, as
   opposed to the colour associated with that item.  For example, the zone
   might be coloured red to indicate four to ten beer drinkers per pub in
   that zone.  The actual value of the statistic might be 9.4 beer drinkers
   per pub.

Variate - A measurable quantity which may take on any of the values within
   a given range, and which has associated with it a specified probability
   function describing the manner in which the permissible values are
   likely to occur.  See also Bivariate, Primary Variate, and Secondary
   Variate.

Viewport - The rectangular area of the colour monitor face selected for
   displaying a specified item.

Window - The rectangular portion of a geographic map which is selected for
   display on the colour monitor.


Zone - A geographic area which is to be considered as a spatial unit.  A
   zone is defined in terms of one or more polygons which form it.
   Statistically, a zone is defined in terms of a single value for each
   variate in question.  This relationship of one variate value per defined
   geographic zone allows zones to be completely and uniformly coloured in
   a map display.  See also Polygon and Variate.

Zone Name - An alphanumeric designation attached to the various
   computerized data associated with a zone.  The zone name facilitates for
   the processor the task of relating various data items to the proper
   zones.