  Interacting with data visualizations without an instrument or touch surface
is typically characterized by the use of mid-air hand gestures. While mid-air
expressions can be quite intuitive for interacting with digital content at a
distance, they frequently lack precision and necessitate a different way of
expressing users' data-related intentions. In this work, we aim to identify new
designs for mid-air hand gesture manipulations that can facilitate
instrument-free, touch-free, and embedded interactions with visualizations,
while utilizing the three-dimensional (3D) interaction space that mid-air
gestures afford. We explore mid-air hand gestures for data visualization by
searching for natural means to interact with content. We employ three studies -
an Elicitation Study, a User Study, and an Expert Study, to provide insight
into the users' mental models, explore the design space, and suggest
considerations for future mid-air hand gesture design. In addition to forming
strong associations with physical manipulations, we discovered that mid-air
hand gestures can: promote space-multiplexed interaction, which allows for a
greater degree of expression; play a functional role in visual cognition and
comprehension; and enhance creativity and engagement. We further highlight the
challenges that designers in this field may face to help set the stage for
developing effective gestures for a wide range of touchless interactions with
visualizations.
