  We present a systematic review on three comparative layouts (i.e.,
juxtaposition, superposition, and explicit-encoding) which are information
visualization (InfoVis) layouts designed to support comparison tasks. For the
last decade, these layouts have served as fundamental idioms in designing many
visualization systems. However, we found that the layouts have been used with
inconsistent terms and confusion, and the lessons from previous studies are
fragmented. The goal of our research is to distill the results from previous
studies into a consistent and reusable framework. We review 127 research
papers, including 15 papers with quantitative user studies, which employed
comparative layouts. We first alleviate the ambiguous boundaries in the design
space of comparative layouts by suggesting lucid terminology (e.g., chart-wise
and item-wise juxtaposition). We then identify the diverse aspects of
comparative layouts, such as the advantages and concerns of using each layout
in the real-world scenarios and researchers' approaches to overcome the
concerns. Building our knowledge on top of the initial insights gained from the
Gleicher et al.'s survey, we elaborate on relevant empirical evidence that we
distilled from our survey (e.g., the actual effectiveness of the layouts in
different study settings) and identify novel facets that the original work did
not cover (e.g., the familiarity of the layouts to people). Finally, we show
the consistent and contradictory results on the performance of comparative
layouts and offer practical implications for using the layouts by suggesting
trade-offs and seven actionable guidelines.
