  This paper presents an interactive technique to explain visual patterns in
network visualizations to analysts who do not understand these visualizations
and who are learning to read them. Learning a visualization requires mastering
its visual grammar and decoding information presented through visual marks,
graphical encodings, and spatial configurations. To help people learn network
visualization designs and extract meaningful information, we introduce the
concept of interactive pattern explanation that allows viewers to select an
arbitrary area in a visualization, then automatically mines the underlying data
patterns, and explains both visual and data patterns present in the viewer's
selection. In a qualitative and a quantitative user study with a total of 32
participants, we compare interactive pattern explanations to textual-only and
visual-only (cheatsheets) explanations. Our results show that interactive
explanations increase learning of i) unfamiliar visualizations, ii) patterns in
network science, and iii) the respective network terminology.
