Visualising MultipleOverlapping HierarchiesMartin Graham, Jessie Kennedy, & Chris Hand Napier University, Edinburgh
Overview Introduction Problem Domain Current visualisation techniques Proposed Techniques Prototype Conclusions
Introduction Taxonomy Royal Botanic Garden Edinburgh Multiple overlapping hierarchies In 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.
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.
Issues for Single Trees Issues arising show that visualising even one tree has problems Leaves displayed - internal structure masked Space issues Occlusion when 3D used So visualising one tree is a problem
Visualisation techniques formultiple trees Two main techniques used: Animation - showing development over time Huang & Eades huge graphs • also Wittenburg’s TreeViewer Small Multiples - showing development over physical space Chi’s Evolution of Web Ecologies Treemaps - Shneiderman & Johnson
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