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Set vs Graph-based visualisations of multiple trees


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AVI 2000 presentation comparing set and graph based visualisation of multiple taxonomic trees

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Set vs Graph-based visualisations of multiple trees

  1. 1. A Comparison of Set-based and Graph-basedVisualisations of Overlapping Classification Hierarchies Martin Graham, Jessie Kennedy & Chris Hand Napier University, Edinburgh
  2. 2. Overview Introduction Problem Domain Similar Approaches Prototype 1 - Graph Prototype 2 - Set (+ example) Testing Conclusion
  3. 3. Introduction Hierarchical information structures are a major topic within Information Visualisation (IV) Cone Trees - Robertson, Mackinlay & Card Tree Maps - Johnson & Shneiderman Multiple hierarchies relatively unexplored Relations (intra- and inter- tree)
  4. 4. Taxonomy Re-classifications of plants A B C D
  5. 5. Tasks for MultipleTaxonomies Taxonomist Requirements Track a particular genus’s siblings and parents Track a higher level (internal) node’s children Compare depths Compare global structures
  6. 6. Previous techniques Animation Strong pre-attentive cues Suited for gradual, not abrupt, changes Shows change between only 2 states at any one point Small Multiples (cf Tufte) Display all structures ‘N’ small multiples = 1/’N’th screen area each
  7. 7. Previous Techniques Wittenburg et al’s Group Asynchronous Browsing on the WWW Combines multiple TreeMaps on top of a MultiTree structure Shows correlations (cross-references) using colour Static colouring only Can show top-level correlations but not for individual parts of hierarchies
  8. 8. Graph-based prototype Combine multiple hierarchies into one graph structure Visualised using spring-mass metaphor Different coloured links & glyphs indicate relationships in different hierarchies Interaction via panning/zooming and filtering of a particular node’s relations
  9. 9. Graph-based Prototype Advantages Integrate multiple hierarchies spatially and temporally Drawbacks Above! Double-edged sword Layout issues Computational complexity
  10. 10. Set-based prototype Sets reflect mental model of taxonomic reasoning Differentiate between categories and the objects we are organising Use colour via linking to indicate correlations Linking applied over a set of hierarchies
  11. 11. Set-based Prototype Advantage of Reflects taxonomist’s mental model This is at the price of Lose a level of detail (unnamed leaves and only one relation set shown at a time) Have to accept restrictions of small multiples However... Clearer visualisation
  12. 12. Prototype Effectiveness Metrics v Empirical Testing Brath’s metrics Suitable for static visualisations Interactive visualisations cause problems Zooming and filtering reduce on-screen data density (but make for a more relevant picture)
  13. 13. Prototype Effectiveness Informal User Testing (cf Nielsen) A handful of typical would-be users Used early in development Task-based observations generate solutions (Monk & Wright)
  14. 14. Prototype Effectiveness Observations Overlapping (occluding) nodes caused confusion in graph prototype Non-leaf (category) nodes in set based prototype indicated by highlighting their descendent leaf nodes, confusing users as to extent of the non-leaf node
  15. 15. Prototype Effectiveness Solutions Ensure that highlighted nodes always displayed on top of unselected nodes Allow user to fine-tune positioning. Non-leaf nodes and leaf nodes to be highlighted in similar fashion
  16. 16. Prototype Effectiveness Outcome Definite preference for set-based visualisation prototype Graph-based visualisation prototype too cluttered, even with zooming/filtering mechanisms More tasks envisaged
  17. 17. Conclusions Constructed 2 prototypes for visualising multiple hierarchies and their correlations Users stated both prototypes enabled them to see information that is not possible with their current system Future work Test prototypes on other information sets
  18. 18. Acknowledgements Royal Botanic Garden Edinburgh EPSRC