Graphics Reference
In-Depth Information
any doubts, our display of choice is
-coords, where the data appear in the form of
squigglyblotches,andwhich(using queries)theMDskilfully dissectsinordertofind
precious hidden secrets.
At this point, it is worth considering how similar queries are performed using
other exploration methodologies, including the ubiquitous spreadsheets. More im-
portantly, which visual clues prompt the use of such queries. A few basics (see
Sect.
.
or the more detailed references Inselberg,
,
) are recalled here.
In
line and other dualities, some but not all actions are
best performed in the dual. he queries, which are the “cutting tools,” operate on
the display (i.e., dual). he design of these queries should exploit the methodology's
strengths and avoid its weaknesses, rather than mimic the action of queries operat-
ing on standard “nondual” displays. Just like a surgeon has many specialized cutting
tools, one of our early sotware versions had lots of specialized queries. However, not
onlywasitdi
culttoclassifyandrememberthemall,buttheystillcouldnothan-
dle all of the situations encountered. Ater experimentation, I opted for a few (three)
intuitive queries, called
atomic
, which can be combined via boolean operations to
form complex intricate cuts. Even for relatively small datasets, the
-coords, due to the point
-coords display
can look uninformative and intimidating. A lack of understanding of the basics of
the underlying geometry and poor query choice can limit the use of
-coords to un-
realistically small datasets.
Summarizing, the requirements for successful exploratory data analysis are:
an informative display that does not lose any of the information about the data,
good query selection,
skilful interaction with the display.
An Easy Case Study: GIS Data
14.2.2
he first admonition is:
do not let the picture intimidate you,
which can easily happen if you take an uninformed look at Fig.
.
, which is the
dataset that wearegoing toexplore.Itconsists ofover
,
measurements with nine
variables;thefirsttwo,
,specifythelocationonthemapoftheportionofSlove-
nia shown in Fig.
.
(let) where seven types of ground emissions have been mea-
sured by satellite. he ground location,
(
X, Y
)
,ofonedataitemisshowninFig.
.
(right), which corresponds to the region shown in the map and remains open dur-
ing the exploration. he query used to select the data item (as shown in Fig.
.
) is
called Pinch. It is activated by the button
P
on the toolbar. Using this query, a bunch
of polygonal lines (i.e., data items) can be selected (they are “pinched” between the
axes). Moving the cursor changes the position of the selected arrowhead, which is
the larger of the two shown. In duecourse various parts of the GUI will be illustrated
(Parallax, proprietary sotware from MDG Ltd., All Rights Reserved, is used with
permission).
(
X, Y
)
