Information Visualization 2 Case Study: Portraying Hierarchies Visualizing hierarchies Variety of techniques Traditional tree views, alternatives, space-filling views Hierarchies Definition Ordering of items in which particular items are parents or ancestors of others Example: File System Folders/Directories with folders/subdirectories and files inside Fall 2002 CS/PSY 6750

Trees Hierarchies often represented as trees Root at top, leaves at bottom Fall 2002 CS/PSY 6750

Sample Representation Fall 2002 CS/PSY 6750

Another Representation Fall 2002 CS/PSY 6750

Another Representation Fall 2002 CS/PSY 6750

Another Representation root Fall 2002 CS/PSY 6750

Another Representation Fall 2002 CS/PSY 6750

Potential Problems Width of fan-out uses real estate Run out of room quickly Fall 2002 CS/PSY 6750

Another Idea CHEOPS Beaudoin, Parent & Vroomen Fall 2002 CS/PSY 6750

Another Idea ConeTree Card, Mackinlay & Robertson Fall 2002 CS/PSY 6750

Another Idea Use hyperbolic geometry Hyperbolic tree Here: Site Lens from www.inxight.com Demo Fall 2002 CS/PSY 6750 Lamping & Rao

Space-Filling Representation Each item occupies an area Children are “contained” under parent Fall 2002 CS/PSY 6750

Treemap Space-filling representation developed by Shneiderman and Johnson Children are drawn inside their parent Alternate horizontal and vertical slicing at each successive level Fall 2002 CS/PSY 6750

Treemap Example File and directory visualizer white-directories color-files level 1 dirs Fall 2002 CS/PSY 6750

Treemap Fall 2002 CS/PSY 6750

Nested vs. Non-nested Treemaps Fall 2002 CS/PSY 6750

Treemap Affordances Good representation of two attributes: color and area Not as good at representing structure What happens if it’s a perfectly balanced tree of items all the same size? Also can get long-thin aspect ratios Fall 2002 CS/PSY 6750

Treemap Variation SmartMoney.com Map of the Market Illustrates stock movements “Compromises” treemap algorithm to avoid bad aspect ratios www.smartmoney.com/marketmap Fall 2002 CS/PSY 6750

Treemap Variation Use 3D shading cues to help convey structure Demo SequoiaView file viewer for Windows Fall 2002 CS/PSY 6750

Another Technique Sunburst What if we used a radial rather than a rectangular space-filling technique? Sunburst Demonstration of system /usr/local/bin/sunburst Fall 2002 CS/PSY 6750

Sunburst Visualizing file and directory structures Root dir at center Color - file type Angle - file/dir size Fall 2002 CS/PSY 6750

Experiment Compare Treemap and Sunburst with users performing typical file/directory- related tasks Evaluate task performance on both correctness and time Small Hierarchy (~500 files) Large Hierarchy (~3000 files) A B A B Fall 2002 CS/PSY 6750

Experiment 60 participants Participant only works with a small or large hierarchy in a session Vary order across participants SB A, TM B TM A, SB B SB B, TM A TM B, SB A 32 on small hierarchies 28 on large hierarchies Fall 2002 CS/PSY 6750

Tasks Identification (naming or pointing out) of a file based on size, specifically, the largest and second largest files (Questions 1-2) Identification of a directory based on size, specifically, the largest (Q3) Location (pointing out) of a file, given the entire path and name (Q4-7) Location of a file, given only the file name (Q8-9) Identification of the deepest subdirectory (Q10) Identification of a directory containing files of a particular type (Q11) Identification of a file based on type and size, specifically, the largest file of a particular type (Q12) Comparison of two files by size (Q13) Location of two duplicated directory structures (Q14) Comparison of two directories by size (Q15) Comparison of two directories by number of files contained (Q16) Fall 2002 CS/PSY 6750

Results Ordering effect for Treemap on large hierarchies Performance trends favored Sunburst, but not clear-cut Subjective preference: SB (51), TM (9), unsure (1) Fall 2002 CS/PSY 6750

Observations SB appeared to convey structure better Participants felt TM conveyed size better, but not bore out Strategies mattered Fall 2002 CS/PSY 6750

SunBurst Negative In large hierarchies, files at the periphery are usually tiny and very difficult to distinguish examples Fall 2002 CS/PSY 6750

Fix: Objectives Avoid use of multiple windows or lots of scrollbars Make small slices bigger Maintain full circular space-filling idea Allow detailed examination of small files within context of entire hierarchy Don’t alter ratios of sizes Avoid use of multiple windows or lots of scrollbars Provide an aesthetically pleasing interface in which it is easy to track changes in focus Fall 2002 CS/PSY 6750

3 Solutions Three visualization+navigation techniques developed to help remedy the shortcoming Angular detail Detail outside Detail inside With Eugene Zhang Proceedings of Information Visualization 2000, Oct. 2000, pp. 57-65. Fall 2002 CS/PSY 6750

Angular Detail Most “natural” Least space-efficient Most configurable by user Fall 2002 CS/PSY 6750

Detail Outside Exhibits non-distorted miniature of overview Somewhat visually disconcerting Focus is quite enlarged (large circumference and 360°) Relatively space efficient Fall 2002 CS/PSY 6750

Detail Inside Perhaps least intuitive and most distorting Items in overview are more distinct (larger circumference) Interior 360° for focus is often sufficient Fall 2002 CS/PSY 6750

Video 4 minutes Fall 2002 CS/PSY 6750

Key Components Two ways to increase area for focus region: larger sweep angle and longer circumference Smooth transitions between overview and focus allow viewer to track changes Always display overview Allow focus selections from anywhere: normal display, focus or overview regions Fall 2002 CS/PSY 6750