HoloGraphs: An Interactive Physicalization for Dynamic Graphs

TL;DR

HoloGraphs addresses the challenge of visualizing dynamic networks by translating time-sliced embeddings into a tangible, transparent 3D-like representation assembled from printed slices. The approach combines virtual embeddings computed with a force-directed layout and anchored to prior timeslices, with physical embeddings and overlays (trajectories, labels) printed on transparent media to preserve spatial perception and enable interaction without electronics. The work demonstrates the method via a Harry Potter character network case study, showing that non-expert users can glean insights into evolving relationships and dynamics. This physicalization-based workflow offers an affordable, accessible avenue to enhance visualization literacy and engagement in education and science communication, with potential applicability to diverse dynamic networks.

Abstract

We present HoloGraphs, a novel approach for physically representing, explaining, exploring, and interacting with dynamic networks. HoloGraphs addresses the challenges of visualizing and understanding evolving network structures by providing an engaging method of interacting and exploring dynamic network structures using physicalization techniques. In contrast to traditional digital interfaces, our approach leverages tangible artifacts made from transparent materials to provide an intuitive way for people with low visualization literacy to explore network data. The process involves printing network embeddings on transparent media and assembling them to create a 3D representation of dynamic networks, maintaining spatial perception and allowing the examination of each timeslice individually. Interactivity is envisioned using optional Focus+Context layers and overlays for node trajectories and labels. Focus layers highlight nodes of interest, context layers provide an overview of the network structure, and global overlays show node trajectories over time. In this paper, we outline the design principles and implementation of HoloGraphs and present how elementary digital interactions can be mapped to physical interactions to manipulate the elements of a network and temporal dimension in an engaging matter. We demonstrate the capabilities of our concept in a case study. Using a dynamic network of character interactions from a popular book series, we showcase how it represents and supports understanding complex concepts such as dynamic networks.

Figures (5)

• Figure 1: A HoloGraph. We display a dynamic graph by producing and embedding the individual timeslices, printing them on transparent media, and arranging them equally spaced. An overlay shows interesting nodes' trajectories over time and per individual timeslice.
• Figure 2: A dynamic graph (a), where connections between nodes and links differ between different points in time, is split up into timeslices , , , , representing the state of the network at different points in time (b). To emphasize nodes of interest ( ), we divide the timeslices into focus (left) and context (right) subgraphs (c). Arranging the slices in parallel creates a space-time cube appearance (d). Individual timeslices can be removed for inspection and global overlays show the focus nodes' movements over time. For illustration purposes and simplicity, each timeslice subgraph shares the same layout. In practice, each timeslice subgraph is laid out semi-independently of the others, resulting in node movement between time points.
• Figure 3: Embeddings for individual timeslices overlaid. The embedding of the subsequent slice is dependent on the previous. Disappearing (1) and appearing (2) links and the subsequent re-embedding causes movement of the nodes (3).
• Figure 4: Physical embeddings for Focus + Context slices as well as Labels + Trajectories overlays. (a) shows a superimposition of the focus subgraph, indicated by larger and colored nodes, and the context subgraph with smaller, faint grey nodes for a single timeslice. (b) shows the global overlays for focus node trajectories and labels.
• Figure 5: Composition of a HoloGraph. Focus slices show the nodes of interest at every timeslice. Context slices can be added to each focus slice individually (a). Node trajectories of focus nodes can be added as a global overlay (b), together with focus node labels (c).