Graphics Reference
In-Depth Information
Recursive Views
10.2.2
Intheintroductionwedescribedtreemodelsasrecursivepartitioningmethods.Con-
sequently it is only natural to display partitions induced by the tree, resulting in an
alternative way of visualizing tree models.In what follows we will describe visualiza-
tion methods that are based on the partitioning aspect of the models instead of the
hierarchical structure.
Sectioned Scatterplots
Splittingrulesareformulated inthecovariate space;thereforeawaytovisualizeatree
modelistovisualize this spacealong with theinducedpartition boundaries. Foruni-
variatepartitioningrulesthoseboundarieslieonhyperplanesparalleltothecovariate
axes.
Duetothisfactwecanusesomethingassimpleasascatterplotasa
-Dprojection.
Inthisview,allsplitsfeaturinganyofthetwoplottedvariablesareclearlyvisible.Such
sectioned scatterplot featuring the first two split variables is shown in Fig.
.
along
with the associated tree.
It is the same model as in Fig.
.
. Each region is denoted by a particular color in
thescatterplot,andpartitionboundariesareaddedbasedonthetreemodel.
he first split of the tree uses an eicosenoic variable to separate oils originating in
northern Italy and Sardinia from other regions. It is clearly visible in the sectioned
scatterplot that this split is indeed very distinctive.
Figure
.
.
[his figure also appears in the color insert.] Sectioned scatterplot (let) showing root splits
and splits in its children of a classification tree (right)
