  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.
