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  <front>
    <journal-meta />
    <article-meta>
      <title-group>
        <article-title>Challenges of Data Physicalization</article-title>
      </title-group>
      <contrib-group>
        <contrib contrib-type="author">
          <string-name>S. Sandra Bae</string-name>
          <email>sandra.bae@colorado.edu</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Danielle Albers Szafir</string-name>
          <email>danielle.szafir@cs.unc.edu</email>
          <xref ref-type="aff" rid="aff0">0</xref>
          <xref ref-type="aff" rid="aff1">1</xref>
        </contrib>
        <contrib contrib-type="author">
          <string-name>Ellen Yi-Luen Do</string-name>
          <email>ellen.do@colorado.edu</email>
          <xref ref-type="aff" rid="aff0">0</xref>
        </contrib>
        <aff id="aff0">
          <label>0</label>
          <institution>University of Colorado, Boulder, ATLAS Institute</institution>
          ,
          <addr-line>1125 18th St. 320 UCB, Boulder CO</addr-line>
          ,
          <country country="US">USA</country>
        </aff>
        <aff id="aff1">
          <label>1</label>
          <institution>University of North Carolina at Chapel Hill</institution>
          ,
          <addr-line>Computer Science, 201 S Columbia St, Chapel Hill NC</addr-line>
          ,
          <country country="US">USA</country>
        </aff>
      </contrib-group>
      <abstract>
        <p>Data physicalization has emerged as a new method to represent and interact with data physically rather than digitally. Physical representations aford visual analysis in comparable ways to traditional, desktopbased visualization by introducing new capabilities, such as facilitating tactile manipulation, accessible interactions, and immersion, that are beyond traditional 2D visualizations. However, physicalization has historically been a niche aspect of visualization research due to its unique challenges. This work discusses the current challenges and highlights three areas where data physicalization can aid existing research thrusts: broadening participation, supporting analytics, and promoting creative expression.</p>
      </abstract>
      <kwd-group>
        <kwd>data physicalization</kwd>
        <kwd>challenges</kwd>
        <kwd>research agenda</kwd>
      </kwd-group>
    </article-meta>
  </front>
  <body>
    <sec id="sec-1">
      <title>1. Introduction</title>
      <p>
        Data physicalization—the practice of mapping data to physical form—sits at the crossroads
of various domains, including data visualization, tangible user interaction, and design [
        <xref ref-type="bibr" rid="ref1">1</xref>
        ].
Data has been traditionally visualized through the desktop model, but current and anticipated
advancements in material science and digital fabrication are radically changing how we can
possibly represent and interact with data. Data physicalization, as a growing field, is not
only introducing new capabilities (e.g., tactile manipulation [
        <xref ref-type="bibr" rid="ref2">2</xref>
        ], accessible interactions [
        <xref ref-type="bibr" rid="ref3 ref4">3, 4</xref>
        ],
immersion [
        <xref ref-type="bibr" rid="ref5">5</xref>
        ]), but also expanding academic discourse on how we traditionally view data [
        <xref ref-type="bibr" rid="ref6">6</xref>
        ].
Despite these advancements, physicalization has historically been a niche aspect of visualization.
      </p>
      <p>
        The challenges of physicalization stem from how the majority of physicalization artifacts
are single prototypes. Without broader synthesis, these individual design explorations prevent
physicalization from maturing on the field’s broader goals, including fabrication development,
theory-building, and ethical and societal impact. To that end, previous research surveyed and
cataloged physicalizations through diferent lenses, including semiotics [
        <xref ref-type="bibr" rid="ref7 ref8 ref9">7, 8, 9</xref>
        ], fabrication
techniques [10], and visualization tasks [11]. However, these past eforts often focus on a
single perspective rather than reflecting on the broader intellectual foundations of the HCI
communities that data physicalization sits upon. From a cross-disciplinary lens, this article
https://sandrabae.github.io/ (S. S. Bae); https://danielleszafir.com/ (D. A. Szafir);
      </p>
      <p>© 2022 Copyright for this paper by its authors. Use permitted under Creative Commons License Attribution 4.0 International (CC BY 4.0).
highlights three promising research areas where data physicalization can aid: broadening
participation, supporting analytics, and promoting creative expression. Thus, this article
discusses the cross-disciplinary challenges that must be addressed for physicalizations to move
from simply vision to being successfully embedded in diferent domain applications.</p>
    </sec>
    <sec id="sec-2">
      <title>2. Background and Motivation</title>
      <p>To invest resources into addressing the challenges outlined in this article, researchers and target
users must see clear benefits in the development of data physicalization. This section briefly
explores the need, purposes, and benefits of physicalizing data.</p>
      <sec id="sec-2-1">
        <title>2.1. Physicalization: Post WIMP Interfaces</title>
        <p>Many data-driven systems use a WIMP (Windows, Icons, Menus, and a Pointer) paradigm and
rely on the graphical user interface (GUI) [12]. However, the WIMP and GUI limit how and
where users can represent and interact with data (i.e., context) [12, 13]. Notably, these
constraints introduce challenges when users (1) work with multi-dimensional data with an inherent
structure and would benefit from physical models (e.g., high-fidelity, material-realistic surgical
models) compared to 2D graphical renditions or (2) work in contexts where the traditional
GUI is infeasible (e.g., robotic operators supervising in an outdoor field test, doctors operating
during surgeries). Data physicalizations provide the opportunity to fundamentally transform
human interactions with data. By removing the constraints of the pixels and moving data
representations from flat displays into the physical world, data interactions become more inclusive
[14, 15], and we can broaden the ways we can experience and communicate data [16, 17, 18].</p>
        <p>Knowing systematically how physicalization difers or fits within existing visualization
tools requires a deep understanding. Due to physicalization’s cross-disciplinary nature, this
understanding calls for careful considerations that are beyond conventional data visualizations
[11, 19]. For example, while all visualizations must consider the expressivity of their designs
(e.g., data encoding and data interactions), physicalization designers must also be mindful of
the physicalization’s structural and contextual considerations [19].</p>
        <p>Each data physicalization artifact (un)consciously reflects diferent community perspectives
and values [19]. For example, physicalizations from the data visualization community mainly
focus on how to efectively encode data and support analytical tasks. Physicalizations from
the tangible user interface community explore how to amplify the capabilities of the human
body and physical world for interaction design, while artifacts from design investigate how to
identify and leverage a material’s potential. In short, by developing this deeper understanding,
the opportunities data physicalization, as a field, faces might be both expanding (through values
of diferent disciplines) and converging (through the advances in the field).</p>
      </sec>
      <sec id="sec-2-2">
        <title>2.2. Purposes and Benefits: Situating within Existing Research Thrusts</title>
        <p>
          Through this cross-disciplinary lens, the opportunities data physicalization afords generally
align with three existing research thrusts: broadening participation, supporting analytics,
and promoting creative expression. These research thrusts are derived from the authors’
meta-content analysis of tasks presented in Bae et. al’s design space for physicalizations [19].
This work aims to outline the emerging trends of physicalization research since Jansen et
al.’s formalization of the field in 2015 [
          <xref ref-type="bibr" rid="ref1">1</xref>
          ]. Thrust 1 focuses on understanding how physical
representations can enable broader participation when working with data. Thrust 2 focuses on
how to employ fabrication techniques to eficiently represent and interact with data and how to
leverage the analytical afordances of physical representations. Thrust 3 explores how data acts
as a material to create new designs.
        </p>
        <p>
          Thrust 1: Broadening Participation. The use and need for visualizations and data are not
just confined to experts anymore. But the design of visualizations holds implicit assumptions
about the user’s sensory, cognitive, and motor abilities [15]. Scholarship highlights how
exclusively digital solutions present challenges and limitations to certain populations (e.g., people
with low vision or visual impairments [
          <xref ref-type="bibr" rid="ref4">4, 20</xref>
          ], children [21]). These challenges present the need
to further investigate how to expand the ways we can interact with data and visualizations.
        </p>
        <p>One form of exploration is focusing on non-traditional audiences: children. The novelty
of physicalizing data ofers an unprecedented method for children to engage with and better
understand data. For example, Data is Yours is a toolkit [21] made out of everyday materials
(e.g., paper, cardboard). The toolkit explores how constructionist practices can broaden ways
of introducing children to data visualization concepts, and in turn, cultivate their data
visualization literacy (DVL). Past work on children’s DVL has often relied on exclusively digital
solutions, where they may come of as “black boxes” to young children and limit their embodied
experiences[22]. Physical representations, in contrast, enable children to engage in embodied
learning that would not be possible with a 2D screen.</p>
        <p>
          Thrust 2: Supporting Analytics. Rooted in visualization, Jansen et al. [
          <xref ref-type="bibr" rid="ref1">1</xref>
          ] formally
defined physicalization as a research field that focuses on “how computer-supported, physical
representations of data (i.e., physicalizations) can support cognition, communication, learning,
problem solving, and decision making”. As such, researchers investigated how to leverage
physicality for data representation [23, 24, 25], data interaction [
          <xref ref-type="bibr" rid="ref2">26, 27, 2</xref>
          ], and social purposes
[28, 29].
        </p>
        <p>But there continue to be underlying challenges, namely understanding which datasets would
be the most meaningful to analyze and knowing how to analyze them physically. By looking at
other disciplines, we see possibilities in how physicality may aid in pre-surgical planning [30]
or analyzing star formation [31]. But once a dataset has been chosen, it is important to know
how physicalization interfaces can support rich, dynamic interactions. Visualization shows the
importance of dynamic interactions, where analysts engage in a series of interactions when
exploring a dataset [32]. This reflects findings on how the number of data interactions a system
supports afects the richness of the data exploration [ 19]. Thus, there is a rich opportunity
to explore how physicalizations utilizing state-of-the-art fabrication techniques can support
analytics and decision-making processes.</p>
        <p>
          Thrust 3: Promoting Creative Expression. Engineers, scientists, and artists are building
physical artifacts guided by data [33, 34]. The cross-disciplinary space of data physicalization
reveals examples of physical artifacts that are encoded with data but do not meet Jansen et al.’s
utilitarian definition of data physicalization (Thrust 2). Collectively, these artifacts are examples
where data is used as a material source when making. Like a craftsman working with their
surrounding materials, data is now another material source and is part of the artisanal spirit
when making. For instance, Friske et al. created a data-encoded scarf where “[d]ata became one
material among others, no more or less important in design” [34]. The discussion reveals how
the authors had to negotiate between how accurately they wanted to encode the data in the
physical representation versus embracing the spirit of the material (i.e., yarn). This perspective
stands in contrast to Thrust 2, which is more cognitively oriented. In this case, data encoding is
prioritized in terms of its efectiveness in helping users carry out their analytical tasks, such
as comparing values or estimating correlations [
          <xref ref-type="bibr" rid="ref1">1</xref>
          ]. As data continues to be embedded in our
world, Thurst 3 highlights how data-driven artifacts can be used for customization [35, 36] or
hedonic purposes [37, 38].
        </p>
      </sec>
    </sec>
    <sec id="sec-3">
      <title>3. Challenges</title>
      <p>By understanding the benefits of physicalizing data (Section 2.2), we can highlight emerging
challenges. The presented challenges are not comprehensive nor do they discuss the downsides
of physicalizations (e.g., issues related to sustainability and product lifecycle). Rather they aim
to open discussions on where research eforts should be targeted based on current trends.</p>
      <p>C1: Fabrication: Constructing data physicalizations involves a large design space [19],
which includes but is not limited to material choice, scale [39], interactions, and data encoding.
This introduces combinatorial possibilities that a user has to consider when designing
physicalizations. In addition, despite material and fabrication advancements, we lack fundamental
guidance on how to leverage the analytical afordances of physical representations. This also
highlights a technical challenge in understanding how to accurately map data to the given
material. Users will need to consider the tradeofs between material properties (e.g., fluid-based
systems [40] and smart materials over electromechanical and magnetic actuators [41]).</p>
      <p>C2: Interpretation: Currently, there is no formal design language (analogous to Grammar of
Graphics [42]) that helps users interpret data physicalizations. Many data physicalizations either
use conventional 2D data visualization representations or are idiosyncratic where each encoding
is unique to the creator. This starkly contrasts with the field of information visualization where
there is an existing design language to help communicate data findings.</p>
      <p>The two challenges are closely intertwined due to their overlapping focus on data encoding.
For instance, interpreting a physicalization will ultimately arise from its fabrication technique.
However, understanding the scope of each challenge can help tackle its associated problems.
E.g., How would the interpretation of a physicalization change if only the fabrication method
changed (e.g., CNC, cast and molding, 3D printing, papercraft)? Through this process, one may
uncover diferent physical afordances or values [ 43] of each fabrication technique.</p>
    </sec>
    <sec id="sec-4">
      <title>4. Conclusion</title>
      <p>Data is ubiquitous where it is now woven into the fabrics of our everyday life. However,
traditional methods of visualizing data digitally limit how we can represent and interact with
data. Physicalization aims to expand this efort, but the field faces challenges due to its
crossdisciplinary nature. This article discusses the benefits and purposes of physicalizing data to
help invest eforts in addressing the outlined challenges. But these challenges will, no doubt,
evolve as technology matures, society changes, and applications of physicalization concretize.
To facilitate this maturation, this work serves as a discussion point to shape the field’s future.</p>
    </sec>
    <sec id="sec-5">
      <title>Acknowledgments</title>
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