Who is the Audience? Designing Casual Data Visualizations for the 'General Public'

Casual data visualizations play a vital role in communicating data to lay audiences. Despite this, little is known about how data visualization practitioners make design decisions based on their envisioned target audiences using different media channels. We draw on the findings of a semi-structured interview study to explore how data visualization practitioners working in various settings conceptualize and design for lay audiences and how they evaluate their visualization designs. Our findings suggest that practitioners often use broad definitions of their target audience, yet they stress the importance of 'knowing the readers' for their design decisions. At the same time, commonly used evaluation and feedback mechanisms do not allow a deep knowledge of their readers but rely instead on tacit knowledge, simple usage metrics, or testing with colleagues. We conclude by calling for different forms of visualization evaluation that are feasible for practitioners to implement in their daily workflows.