  To facilitate the reuse of existing charts, previous research has examined
how to obtain a semantic understanding of a chart by deconstructing its visual
representation into reusable components, such as encodings. However, existing
deconstruction approaches primarily focus on chart styles, handling only basic
layouts. In this paper, we investigate how to deconstruct chart layouts,
focusing on rectangle-based ones, as they cover not only 17 chart types but
also advanced layouts (e.g., small multiples, nested layouts). We develop an
interactive tool, called Mystique, adopting a mixed-initiative approach to
extract the axes and legend, and deconstruct a chart's layout into four
semantic components: mark groups, spatial relationships, data encodings, and
graphical constraints. Mystique employs a wizard interface that guides chart
authors through a series of steps to specify how the deconstructed components
map to their own data. On 150 rectangle-based SVG charts, Mystique achieves
above 85% accuracy for axis and legend extraction and 96% accuracy for layout
deconstruction. In a chart reproduction study, participants could easily reuse
existing charts on new datasets. We discuss the current limitations of Mystique
and future research directions.
