EDGE-EQUALIZED TREEMAPS - Information Visualisation: Techniques, Usability and Evaluation - page 108

C HAPTER S IX
E DGE -E QUALIZED T REEMAPS
A IMI K OBAYASHI , K AZUO M ISUE
AND J IRO T ANAKA
Abstract
A Treemap is a visualization method for hierarchical structures in which
nodes are drawn as rectangles and arranged in a nested style. Variations of
Treemaps have been developed to represent different types of data. In this
chapter, we propose the Edge-Equalized Treemap, a representation
suitable for embedding visual data, such as a bar chart, in leaf rectangles.
This representation is characterized by leaf rectangles of equal widths.
Because their widths are equal, the scale intervals of charts in a leaf
rectangle can be equalized, meaning that we can compare charts by simple
visual inspection. We compare the Edge-Equalized Treemap with existing
layout methods and demonstrate the usefulness of our approach.
1 Introduction
Many types of data can be categorized as hierarchical structures. In the
field of graph theory, these are called rooted trees. Hierarchical structures
consist of one or more elements, called nodes. Each node has at most one
parent node, and the only node that does not have a parent is a root node.
We refer to nodes that have no children as leaf nodes. A node that is
neither the root nor a leaf is a branch. For example, the structure of
directories and company organizations is hierarchical. In a directory, each
file or directory is a node, and all files are leaf nodes. In a company
organization, each department or person is a node, and all individuals are
leaf nodes. Some hierarchical data have leaf nodes with different weights.
For instance, the sizes or priorities of files in a directory structure and the