  Network visualization allows a quick glance at how nodes (or actors) are
connected by edges (or ties). A conventional network diagram of "contact tree"
maps out a root and branches that represent the structure of nodes and edges,
often without further specifying leaves or fruits that would have grown from
small branches. By furnishing such a network structure with leaves and fruits,
we reveal details about "contacts" in our ContactTrees that underline ties and
relationships. Our elegant design employs a bottom-up approach that resembles a
recent attempt to understand subjective well-being by means of a series of
emotions. Such a bottom-up approach to social-network studies decomposes each
tie into a series of interactions or contacts, which help deepen our
understanding of the complexity embedded in a network structure. Unlike
previous network visualizations, ContactTrees can highlight how relationships
form and change based upon interactions among actors, and how relationships and
networks vary by contact attributes. Based on a botanical tree metaphor, the
design is easy to construct and the resulting tree-like visualization can
display many properties at both tie and contact levels, a key ingredient
missing from conventional techniques of network visualization. We first
demonstrate ContactTrees using a dataset consisting of three waves of 3-month
contact diaries over the 2004-2012 period, then compare ContactTrees with
alternative tools and discuss how this tool can be applied to other types of
datasets.
