Graphics Reference
In-Depth Information
that they are easier to read. he subtitle of Fig.
.
is also more heavily emphasized
by using a bold font face. heTrellis defaults extend to selections of plotting symbols
and colours in plots of multiple data series, which are chosen so that different data
series can be easily distinguished by the viewer.
User Interface
3.1.2
Asometimes controversial aspectof statistical graphics sotware isthe userinterface.
he choice is between a command line, where the user must type textual commands
(or function calls), and a graphical user interface (GUI), consisting of menus and
dialogue boxes. A batch system is considered to be a command-line interface; the
importantpointisthattheuserhastodoeverythingbytypingonthekeyboardrather
than by pointing and clicking with a mouse. Oten both a command line and a GUI
will be offered.
heinterface toapieceofsotware isconceptually orthogonal tothesetoffeatures
thatthesotwareprovides,whichisourmainfocushere.Nevertheless,ineachsection
of this chapter we will briefly discuss the user interface because there are situations
where the interface has a significant impact on the accessibility of certain features.
For the purpose of producing complete plots, the choice of user interface is not
very important. Where one system might have an option on a GUI menu to produce
a histogram, another system can have a command or function to do the same thing.
With R, the standard interface is a command line, but a number of GUI options
exist, notably Rcmdr (Fox,
), JGR (Helbig et al.,
) and the standard GUI on
the Mac platform (Iacus and Urbanek,
).
Customization
3.2
Let us assume that your statistical sotware allows you to produce a complete plot
from a single command and that it provides sensible defaults for the positioning and
appearance of the plot. It is still quite unlikely that the plot you end up with will be
exactlywhatyouwant.Forexample,youmaywantadifferentscaleontheaxes,orthe
tickmarksindifferentpositions, ornoaxesatall.Aterbeingabletodrawsomething,
thenextmostimportantfeatureofstatistical graphicssotwareistheabilitytocontrol
what gets drawn and how it gets drawn.
Setting Parameters
3.2.1
For any particular piece of output, there will be a number of free parameters that
must be specified. As a very basic example, it is not su
cient to say something like
'I want to draw a line'; you must also specify where the line should start and where
it should end. You might be surprised how many free parameters there are in even
simplecaseslike this;inordertofully specifythedrawingofasinglestraight line,itis
necessary to provide not only a start and end point, but a colour, a line style (perhaps
