U.S. Department of Energy

Pacific Northwest National Laboratory

The “y” of it Matters, Even for Storyline Visualization

Publish Date: 
Friday, September 22, 2017
Storylines are adept at communicating complex change by encoding time naturally on the x-axis and using the proximity of lines in the y direction to encode an interaction between entities at a particular time. The original definition of a storyline visualization requires data defined in terms of explicit interaction sessions. A more relaxed definition allows storyline visualization to be applied more generally (e.g., for geo-temporal analysis, multivariate time-series analysis) by visualizing how entities' states collectively change over time. However, this creates questions about how the y-coordinate should encode interactions when an interaction is tied to a particular place or state. To answer this question, we conducted a design study where we considered two design alternatives within a geo-temporal analysis tool written to solve part of the VAST Challenge 2014. We measured the performance of users at overview and detail oriented tasks between two storyline layout algorithms. We compared a traditional storyline layout algorithm (conforming to the current assumed aesthetic and design criteria from the literature) to an alternative layout algorithm where the y-coordinate exactly encodes the state of the entity. To the best of our knowledge, this paper is the first work to question the design principles for storyline visualization, and what we found surprised us. For overview tasks with the alternative layout, which has a consistent encoding for the y-coordinate, users performed significantly better (p<.05) than the storyline layout based on existing design constraints and aesthetic criteria. There was no significant difference in user performance between the two layout algorithms for detail oriented tasks. Our empirical findings were also supported by first-hand accounts taken from interviews with multiple expert analysts, who suggested that the inconsistent meaning of the y-axis was misleading. These findings led us to design a new storyline layout algorithm that is a ``best of both'' where the y-axis has a consistent meaning but aesthetic criteria (e.g., line crossings) are considered.
Arendt DL, and MA Pirrung. 2017. "The “y” of it Matters, Even for Storyline Visualization." In IEEE VAST 2017.
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