  Data visualization is becoming an increasingly popular field of design
practice. Although many studies have highlighted the knowledge required for
effective data visualization design, their focus has largely been on formal
knowledge and logical decision-making processes that can be abstracted and
codified. Less attention has been paid to the more situated and personal ways
of knowing that are prevalent in all design activity. In this study, we
conducted semi-structured interviews with data visualization practitioners
during which they were asked to describe the practical and situated aspects of
their design processes. Using a philosophical framework of design judgment from
Nelson and Stolterman [23], we analyzed the transcripts to describe the volume
and complex layering of design judgments that are used by data visualization
practitioners as they describe and interrogate their work. We identify aspects
of data visualization practice that require further investigation beyond
notions of rational, model- or principle-directed decision-making processes.
