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                2 Main Approaches
   • Connection (node & link)
         •                                  A
          outliner
                                          B    C
   • Containment (node in node)
         • Venn diagram                A
                                          B     C
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                              Tasks
      • Help understand node characteristics or 
         tree structure?
      • Some kinds of tasks:
          – Find a node
          – Revisit node
          – List node ancestors
          – Understand local topology
          – Understand global topology
      • Different Trees are good for different tasks
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      Why is tree visualization hard?
         – Structure AND items (Structure 
           harder, consumes more space)
         – Scaling: data size grows very quickly 
           (exponential)
            • #nodes = bheight
         – How to provide Context (when focus 
           changes)
         – May be multiple hierarchies
         – May be multiple focuses
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                     Current Status
      • Many 2D and 3D hierarchy visualizations
         – Each works for some tasks and some scales
         – Very few have had user testing
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