  We describe a new visualization tool, dubbed HCMapper, that visually helps to
compare a pair of dendrograms computed on the same dataset by displaying
multiscale partition-based layered structures. The dendrograms are obtained by
hierarchical clustering techniques whose output reflects some hypothesis on the
data and HCMapper is specifically designed to grasp at first glance both
whether the two compared hypotheses broadly agree and the data points on which
they do not concur. Leveraging juxtaposition and explicit encodings, HCMapper
focus on two selected partitions while displaying coarser ones in context areas
for understanding multiscale structure and eventually switching the selected
partitions. HCMapper utility is shown through the example of testing whether
the prices of credit default swap financial time series only undergo
correlation. This use case is detailed in the supplementary material as well as
experiments with code on toy-datasets for reproducible research. HCMapper is
currently released as a visualization tool on the DataGrapple time series and
clustering analysis platorm at www.datagrapple.com.
