  As online news increasingly include data journalism, there is a corresponding
increase in the incorporation of visualization in article thumbnail images.
However, little research exists on the design rationale for visualization
thumbnails, such as resizing, cropping, simplifying, and embellishing charts
that appear within the body of the associated article. Therefore, in this paper
we aim to understand these design choices and determine what makes a
visualization thumbnail inviting and interpretable. To this end, we first
survey visualization thumbnails collected online and discuss visualization
thumbnail practices with data journalists and news graphics designers. Based on
the survey and discussion results, we then define a design space for
visualization thumbnails and conduct a user study with four types of
visualization thumbnails derived from the design space. The study results
indicate that different chart components play different roles in attracting
reader attention and enhancing reader understandability of the visualization
thumbnails. We also find various thumbnail design strategies for effectively
combining the charts' components, such as a data summary with highlights and
data labels, and a visual legend with text labels and Human Recognizable
Objects (HROs), into thumbnails. Ultimately, we distill our findings into
design implications that allow effective visualization thumbnail designs for
data-rich news articles. Our work can thus be seen as a first step toward
providing structured guidance on how to design compelling thumbnails for data
stories.
