glossary

GLOSSARY

3D	'Three-dimensional' - a term used to describe attempts to draw a three- dimensional object such as a curved surface or xyz graph on a two- dimensional screen or piece of paper. Also called 'two-and-a-half dimensional'.
4D	'Four-dimensional' - a 3D diagram in which colour is used to depict the variation of a fourth variable.
A0/A1/A2/A3/A4/A5	Standard paper sizes: A4 is 297mm by 210 mm; A3 is 420mm by 297mm with sizes A2, Al and A0 progressively doubling. A5 is 210mm by 148mm
area chart	A chart in which the area of interest is shaded in solid colour: useful for capturing attention but should be used sparingly for best effect.
ASCII	The American Standard Code for Information Interchange - a standard for the representation of textual characters held in a computer system. For example the ASCII value for 'A' is 65, or 01000001 in binary.
bar chart	A 'horizontal histogram', in which data values are represented by horizontal bars. Not used widely, but particularly effective where each individual data point has to be named. See also column chart.
bramble chart	See cluster chart.
business graphics	A general term for methods of presenting data in a formal, structured fashion - such as a line graph, bar chart, pie chart or histogram. See also "creative graphics".
Cartesian coordinates	A measurement system for defining the position of a point with respect to two (or more) straight axes at right angles to each other. This is the commonest coordinate system, the main alternative being polar coordinates
CGM	'Computer Graphics Metafile', an ISO standard by which pictorial information can be stored in a computer file, in which form it can be transferred and reconstituted. CGM is more commonly used for transferring graphical images between software packages than for sending it to output devices such as plotters.
chart	A general term indicating any drawing, graph, image, text, or combination of these elements.
CHEST	Combined Higher Education Software Team. CHEST arranges and administers software deals on behalf of the UK academic community. The CHEST Software Directory is available on-line through the NISS Gateway, and in book form.
clip art	Collections of graphic images or symbols stored in computer form which can be readily incorporated into more complex diagrams, documents or presentations to enliven their appearance. Clip art libraries are available to cover most everyday items and many specialised ones. Care should be taken to observe any copyright restrictions when using clip art.
cluster chart	A form of chart suitable for depicting data which only falls into a few restricted categories, such as 'normal', 'high' or 'low'. The x axis is then usually descriptive rather than numeric. Used particularly in medical and biological work.
column chart	A chart in which data values are represented by vertical columns: histograms are a specific class of column chart used in statistical work. See also bar chart.
contour chart	A method for depicting 3D data such as the heights of a landscape, or in general, for any measurements which are a function of two other, independent, variables. Thus each point is specified by three measurements, two for its position (x,y) and one for its actual value (z). An Ordnance Survey map is a contour chart.
creative graphics	A general term for informal and unstructured graphical presentation, not usually representing any pre-existing data. Common examples are drawings and diagrams produced by hand. See also "business graphics".
curve-fitting	The attempt to find a pattern in data by drawing a line through a set of points so that it goes as close as possible to all of them. This could be a straight line but is more generally a curved one, ideally with an underlying equation which would help to analyse the data.
DDE	See "Dynamic Data Exchange".
device driver	A software module which accepts input in some general form and converts it into specific instructions which are sent to a specific printer, plotter or other output device. For example many graphics packages and word-processors generate their output in device-independent form and rely on specific device drivers to produce the actual output. In this method of working every device must have its own specific device driver.
device independence	The operational mode of many graphics and word-processing packages, which do not produce their output in a form which can be sent to any output device (such as a plotter or printer), but which contains all the necessary information from which a device driver can generate the required output on information from which a device driver can generate the required output on a particular device.
digitiser	A device which converts graphical input into a digital form which can be manipulated in a computer. It consists of a tablet on which a diagram can be mounted, and a pen-like stylus which can be traced around the diagram, Producing digital measurements which are fed into the computer.
digitising tablet	A graphical device which enables pictorial information to be input to a computer. It is especially appropriate for line-based pictures (for example mapping boundaries). The process involves drawing over each line with a special stylus or mouse device.
dithering	The technique of manipulating patterns of dots produced by a printer to generate more colours or shades of grey than it should be capable of. For example if a black-and-white printer can print a small box as a pattern of black and white dots, the overall appearance of the box will be grey, its precise shade depending on the relative proportions of the black and white dots. Similarly a simple colour ink jet printer can produce various shades of orange from patterns of red and yellow dots. This is a very effective technique, but the penalty is loss of resolution in the final image.
dot-matrix printer	A (cheap, noisy and comparatively slow) printing device in which text and graphics are produced by an array of pins forcing a printer ribbon against paper. The alternative is a 'non-impact printer' such as an 'inkjet printer' (relatively cheap) or 'laser printer' (relatively expensive).
dots per inch	('Dpi') a measure of the resolution of an output device such as a computer screen or laser printer, which effectively shows the size of the dots it uses to generate characters and graphics. The bigger this number, the smaller the dots and the finer the resolution. For example, apple mac screens have 72 dpi, and most laser printers have 300 dpi, with 600 dpi starting to appear in desktop machines. The very best publications require at least 1200 dpi devices.
dpi	Acronym for dots per inch.
Dynamic Data Exchange	A proprietary method of linking the data in one application to a graphical or other display in another application. When the data is changed in the first program, the display in the second is updated automatically, allowing a single master set of data to be used for all purposes.
enveloping	"Envelope-ing" - distorting a graphical image by fitting it into a non- rectilinear shape, or envelope.
error bars	Lines which are added to the data points in certain types of graph to indicate the margin of error in that point - that is, the range within which it lies. An error bar indicates the range of values when several measurements are used to generate a single point on a graph, or the maximum possible error in measuring or calculating the position of the point.
font	See ‘typeface'.
functionality	A measure of the capability of, or range of facilities available in, an item of software or hardware. Modern computer packages and equipment tend to have much better functionality than older ones, and expensive ones greater functionality than cheaper ones.
Graphical User Interface	A characteristic style of user-program interface in which the computer is controlled graphically - by a mouse acting through windows and icons - rather than by issuing it with textual commands. See also WIMP.
grey scale	The ability of a black-and-white printer or screen to display shades of grey.
GUI	Graphical User Interface, pronounced "gooey". See also WIMP.
hardcopy	Output on a permanent medium such as paper, transparency, film or video, as opposed to temporary output to a computer screen.
histogram	A special form of 'column chart', particularly used in statistical applications, using vertical columns to display the value of the data point or the average value of a range of data points in a limited set of classes.
hot link	A connection between data in one program and its use in another, for example allowing data to be changed in a spreadsheet, whereupon a separate graphics or DTP package - connected to the first by a hot link - automatically changes its representation of that data.
HPGL	'Hewlett-Packard Graphics Language' - a de facto standard language with which to control pen plotters, which is also accepted by a number of non- pen devices such as laser printers and electrostatic plotters.
image	( 1) any graphic item, made up of any graphical elements including text. (2) a precise copy of the contents of a computer's memory, elsewhere in memory or on a disk.
impact devices	Printing devices in which text and graphics are produced by an array of pins forcing a printer ribbon against paper. They tend to be cheap, but produce low-quality output and are noisy and comparatively slow.
inkjet printer	Drops of ink at the paper, typically on a 300 dpi matrix. Results are almost as good as a cheap laser printer's, though the ink tends to spread a little, and will run if it gets wet.
Laser printer	A non-impact printing device which operates in similar fashion to a photocopier, in which a laser draws the image of a page on a photosensitive drum which then attracts toner on to the paper, where it is subsequently bonded by heating. Now the most popular type of printer for reasonable
LED printer	Very similar to a laser printer, but using leds (light-emitting diodes) rather than a laser to create the electrostatic charge on the drum.
Line art	A diagram which consists only of lines and text, requiring no complex grey level or colour shading.
Line chart	One of the commonest forms of graph, particularly favoured by scientists, with data points displayed against X and Y axes and all the points connected with a single line. The points themselves need not be shown. Alternatively, all the data points may be shown and a line drawn which doesn't necessarily go through them all but which gives a reasonable 'best fit' to them all.
media	Plural of 'medium', referring to the types of material on which computer output can be stored. The commonest media are disks (hard and floppy), magnetic tape (reel and cartridge), optical disks, punched paper and punched cards, ordinary paper, photographic film, video, and semiconductor 'flash-cards'.
metafile	A file which contains a description of a picture or set of pictures in a well- defined, formal manner. This allows diagrams to be transferred between different graphics packages, and also allows programs to ignore the specific details of particular output hardware - but just use a common 'device- driver' to translate the metafile into printer-specific instructions.
mirroring	Transforming a graphical image into its horizontally reversed form, as though reflected in a mirror.
mono(chrome)	An output device which can only show one colour, though possibly in several shades. Monochrome printers and some screens tend to be black- and-white.
non-impact devices	Printers and plotters which do not use physical force to transfer ink to paper, common examples being inkjet, thermal-wax and laser printers.
paired bar chart	A special kind of 'bar chart' which uses horizontal columns in pairs to emphasise the differences in measurements taken at two different times, places, experiments etc.
pen plotter	A reasonably cheap type of output device which uses pens to draw graphic images on paper. It is fine for producing smooth lines and is therefore the natural way to draw line charts, but it has few colours, is not sensible for area fill, and is slow for complex drawings.
perspective	A technique for making three-dimensional objects look more natural when represented on paper or screen, by for example making distant objects smaller than closer ones, and parallel lines converge in the distance.
pie chart	An effective method of displaying (preferably no more than) about six variables, rather like looking down on a circular apple pie which has been cut into slices. The size of each slice reflects the size of each variable.
polar chart	A chart on which data points are plotted in polar coordinates rather than 'Cartesian coordinates'. Each point is defined in terms of its distance from the centre of a circle and the angle a notional connecting line makes to the horizontal.
PostScript	A de facto standard page-description language from the Adobe Corporation, which is now the most widely used way of sending text and graphics to printers such as laser printers - many of which now have postscript interpreters built-in for speed and flexibility.
prepress	Final preparation of material to be printed to the highest standards, probably by an external, professional printer. This includes the specification of all the fonts and graphics used in a document.
presentation	In the normal sense of the word, a presentation is some kind of talk to an audience, possibly enhanced with visual or audio material. A 'presentation package' runs on a computer to assist with the production of illustrative material to be used in a presentation, either in generating such aids as overhead or 35mm transparencies, or - increasingly - used at the presentation itself, with the on-screen images viewed directly by the audience.
QC chart Quality control chart	A chart which shows the acceptable range of measurements, perhaps on some manufactured item or experimental data, on which actual measurements can be plotted to show whether the manufacture or experiment is proceeding satisfactorily.
raster	The technique of building up a graphical image as a series of on/off or coloured dots along a set of lines on a screen or other output device. A television set is the commonest form of raster device. In a laser printer or computer display, for example, the image is built up by a signal which is swept along each line in succession, and variously attenuated to produce the required pattern. The alternative method of producing images is 'vector'.
resolution	The fineness of detail which a computer device can detect or produce. For example a high-resolution screen or printer can show fine detail, and a high- resolution scanner or digitiser can detect fine detail.
rotation	Transforming a graphical image by rotating it about some axis, to some degree. 'Mirroring' is a special case of rotation.
scanner	A device which scans a light across a page of text or graphics and feeds a digitised representation of the image into a computer for storage or further processing. Scanners are typically flat-bed (like a photocopier), rotating- drum, or hand-held. If the image is text, there are software packages which can convert it from an image to actual characters which can for example be loaded into a word-processor.
scatter chart	A classic 'x vs y' graph consisting of two axes, with each data point marked with its own symbol: like a 'line chart' but without the connecting lines.
site licence	An agreement between a software publisher and an educational establishment which allows software to be acquired at a reduced price, on condition that it is only used for academic, non-commercial purposes.
skewing	Transforming a graphical image by distorting it about some axis, to some degree. For example, a square can be skewed into a diamond shape.
subscript	Text which is written on a lower baseline, and usually in a smaller font, than its surrounding text, as for example the x in lx.
superscript	Text which is written on a higher baseline, and usually in a smaller font, than its surrounding text, as for example the 2 in x2.
text chart	A chart consisting mainly or exclusively of text, added graphical elements including colour, font and background. Text charts are commonly used on overhead and 35mm transparencies and in 'presentation' packages, for example.
typeface	A character design, specifying the shape of all the upper and lower case characters, numerals and punctuation symbols. Different typefaces are useful in different contexts, for example in running text or in headlines, and to give an old-fashioned, or conservative, or modem, or striking appearance. Commonly used typefaces include times, helvetica and courier. Each typeface is actually a family of individual 'fonts', each of which represent the typeface in a particular size (such as 12 point) and style (such as bold or italic). The words 'font' and 'typeface' are increasingly - and inaccurately - used interchangeably.
Uniras	A large and powerful graphics package available on a range of computer platforms to enable users to generate most types of graphical output
vector	A straight line drawn from one point to another point. Vector devices, of which the commonest type is the 'pen plotter', are designed specifically to draw or plot vectors, making them ideal for graphical objects such as line charts which consist only of lines. The more versatile alternative is a 'raster' device.
WIMP	"Windows, /images/, Menus and Pointer", or "Windows, /images/, Mouse and Pull-down menus" This is a graphical interface which makes access to computers much more straightforward and intuitive than the main alternative, the command-line interface. The WIMP interface has been used on Apple Macintosh computers since they were invented, and are coming into use on PCs through Microsoft Windows and on Unix and other workstations through the X Window system.
Windowing System	A graphical (GUI) interface to a computer's Operating System, giving the user such features as windows, a mouse and pull-down menus by which to drive the computer, rather than having to type in command words.
workstation	Any computer which can sit on a desk, though usually taken to indicate amore powerful machine such as those from Sun or Silicon Graphics, rather than a less powerful PC or Apple Mac.
WYSIWYG	"What You See Is What You Get" - the description of systems or packages which faithfully represent on the screen what a document will look like when printed.