The Arrangement of Marks Impacts Afforded Messages: Ordering, Partitioning, Spacing, and Coloring in Bar Charts

TL;DR

This paper empirically investigates how the arrangement of elements in bar charts, including ordering, partitioning, spacing, and coloring, influences the messages viewers are likely to notice, providing scalable methods for understanding visualization affordances.

Contribution

It introduces a scalable, empirical method to analyze how visual arrangements in bar charts affect message perception, filling a gap in understanding visualization message affordances.

Findings

Arrangement significantly influences message perception.

Coloring and spacing alter which data aspects are noticed.

The method enables systematic study of visualization message effects.

Abstract

Data visualizations present a massive number of potential messages to an observer. One might notice that one group's average is larger than another's, or that a difference in values is smaller than a difference between two others, or any of a combinatorial explosion of other possibilities. The message that a viewer tends to notice--the message that a visualization 'affords'--is strongly affected by how values are arranged in a chart, e.g., how the values are colored or positioned. Although understanding the mapping between a chart's arrangement and what viewers tend to notice is critical for creating guidelines and recommendation systems, current empirical work is insufficient to lay out clear rules. We present a set of empirical evaluations of how different messages--including ranking, grouping, and part-to-whole relationships--are afforded by variations in ordering, partitioning, spacing, and coloring of values, within the ubiquitous case study of bar graphs. In doing so, we introduce a quantitative method that is easily scalable, reviewable, and replicable, laying groundwork for further investigation of the effects of arrangement on message affordances across other visualizations and tasks. Pre-registration and all supplemental materials are available at https://osf.io/np3q7 and https://osf.io/bvy95 .