Graphics Reference
In-Depth Information
Figure
.
.
Hierarchical cluster tree of US murder rates
intrinsic meaning, but sometimes making room for labels and other information is
su
cient justification.
In some cases, the nodes of hierarchical trees may represent nested collections
of objects. Classification and regression trees, for example, hierarchically partition
asetofobjects.Fortheseapplications, Wilkinson (
)invented atreedisplaycalled
a mobile.Figure
.
shows an example using data on employees of a bank. Each node
contains a dot histogram; each dot represents a bank employee. he dot histograms
arehierarchical;aparenthistogramaggregatesthedotsofitschildren.hehorizontal
branchesrepresentabeambalancingtwosiblingdothistograms.Byusingthismodel,
wehighlightthemarginality ofsplits.hatis,outlying splitsareshitedawayfromthe
bulk of the display. his layout is relatively ine
cient with regard to space, and it is
notwellsuitedtoapolararrangement becausethebalance metaphorhasnomeaning
in that context.
Figure
.
showsanalternative displayforclassification trees (Urbanek
).his
form uses the width of branches to represent the size of subsplits. his tree is similar
to earlier graphics shown in Kleiner and Hartigan (
), Dirschedl (
), Lausen
et al. (
) and Vach (
).
