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

Fall 2002CS/PSY Sample Representation

Fall 2002CS/PSY Another Representation

Fall 2002CS/PSY Another Representation

Fall 2002CS/PSY Another Representation root

Fall 2002CS/PSY Another Representation

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

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

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

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

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

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

Fall 2002CS/PSY Treemap

Fall 2002CS/PSY Nested vs. Non-nested Treemaps Nested Tree-MapNon-nested Tree-Map

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

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

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

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

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

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

Fall 2002CS/PSY Fix: Objectives 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 2002CS/PSY With Eugene Zhang Proceedings of Information Visualization 2000, Oct. 2000, pp Solutions Three visualization+navigation techniques developed to help remedy the shortcoming  Angular detail  Detail outside  Detail inside

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

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

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

Fall 2002CS/PSY Video 4 minutes

Fall 2002CS/PSY 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