visualising multiple overlapping hierarchies

Visualising Multiple Overlapping Hierarchies

Martin Graham, Jessie Kennedy, & Chris Hand

Napier University, Edinburgh

Overview

IntroductionProblem DomainCurrent visualisation techniquesProposed TechniquesPrototypeConclusions

Introduction

Taxonomy Royal Botanic Garden Edinburgh

Multiple overlapping hierarchiesIn general occur where a hierarchical

structure is re-organised Taxonomy (our domain) Document categorisation etc

No current visualisations support them

What is a Taxonomy?

A methodology for classifying data. In our case, botanical specimens.

As knowledge increases or opinions change, new classification hierarchies (taxonomies) are published

These taxonomies co-exist. They do not replace each other.

Leads to accumulation of multiple overlapping taxonomies.

Multiple Classifications

Taxonomists need to..

Track a specimen across several classifications

View the progress of a group of specimens across classifications

Filter out unwanted pieces of information

We require a visualisation that can help taxonomists perform these tasks.

Current paper-based taxonomy

The problem

No current suitable paper-based method for inspecting multiple overlapping taxonomies

Investigate current computer-based visualisations

Previous visualisations

Visualisations have been used for viewing hierarchical structures, e.g. file directories

Examples: Cone Trees - Robertson et al Information Pyramids - Andrews

Cone Trees

© 1991 ACM - Cone Trees: Animated 3D Visualizations of Hierarchical Information - Copy by permission of the Association of Computing Machinery

Andrews’ Information Pyramids

“Information Pyramids” is © IICM, Graz University of Technology, Austria

Issues for Single Trees

Issues arising show that visualising even one tree has problems

Leaves displayed - internal structure masked

Space issuesOcclusion when 3D used

So visualising one tree is a problem

Visualisation techniques for multiple trees

Two main techniques used: Animation - showing development over

timeHuang & Eades huge graphs

• also Wittenburg’s TreeViewer

Small Multiples - showing development over physical spaceChi’s Evolution of Web EcologiesTreemaps - Shneiderman & Johnson

Huang’s on-line visualisation of a website

© Dept. of Computer Science and Software Engineering, University of Newcastle, NSW, Australia

Chi et al’s Web Ecology Viewer

© User Interface Research Group - Xerox PARC

Multiple TreeMap Comparison

© Human-Computer Interaction Laboratory, Dept. of Computer Science, University of Maryland, USA

Issues for multiple trees

Animation Direct visual comparison between two

states only. Works best for gradual changes, not new

structures.Small Multiples

Lack of space on-screen due to repeating data

Lacks strong pre-attentive cues

The Problem to be visualised

Need to develop appropriate visualisations to tackle these problems

Time/space trade-off

Initial Design Sketch (1)

Initial Design Sketch (2)

Ability to track a sub-tree (genus - grouping of specimens) across multiple hierarchies

Initial Design Sketch (3)

Filter out unwanted pieces of information

Prototype

Conclusions

Need for visualising multiple hierarchies

Current visualisation techniques inadequate

Initial solutionsContinuing work

Prototyping User evaluation/feedback

Acknowledgements

Royal Botanic Garden, EdinburghEPSRC

http://www.dcs.napier.ac.uk/~marting