Radial Icicle Tree (RIT): Node Separation and Area Constancy

TL;DR

This paper introduces the radial icicle tree (RIT), a novel visualization that combines the benefits of icicle and sunburst trees by maintaining area constancy and improving node separation, validated through analysis and user evaluation.

Contribution

The paper presents RIT, a new visual representation that transforms icicle trees into circular sectors with area consistency, addressing issues of narrow nodes and size inconsistency.

Findings

RIT improves node separation and size consistency.

User evaluation confirms RIT's effectiveness over traditional icicle and sunburst trees.

Analytical design supports RIT's advantages.

Abstract

Icicles and sunbursts are two commonly-used visual representations of trees. While icicle trees can map data values faithfully to rectangles of different sizes, often some rectangles are too narrow to be noticed easily. When an icicle tree is transformed into a sunburst tree, the width of each rectangle becomes the length of an annular sector that is usually longer than the original width. While sunburst trees alleviate the problem of narrow rectangles in icicle trees, it no longer maintains the consistency of size encoding. At different tree depths, nodes of the same data values are displayed in annular sections of different sizes in a sunburst tree, though they are represented by rectangles of the same size in an icicle tree. Furthermore, two nodes from different subtrees could sometimes appear as a single node in both icicle trees and sunburst trees. In this paper, we propose a new visual representation, referred to as \emph{radial icicle tree} (RIT), which transforms the rectangular bounding box of an icicle tree into a circle, circular sector, or annular sector while introducing gaps between nodes and maintaining area constancy for nodes of the same size. We applied the new visual design to several datasets. Both the analytical design process and user-centered evaluation have confirmed that this new design has improved the design of icicles and sunburst trees without introducing any relative demerit.