Interactive Information Visualization ofOne Million Items

Jean-Daniel FeketeJean-Daniel Fekete

University of MarylandUniversity of Maryland

Scaling issues in Information Visualization

• Seeing more data items or more dimensions• No aggregation, no sampling

• What are the limits?• Technical

• screen resolution / dimension, 10ms redisplay speed

• Perceptual• visual system accuracy, perception-action loop speed

• Cognitive• how much can we understand and how long does it

take?

Visualizing one million items

• Treemap of a Unix file system containing 1 million files

• Rectangle sizes related to file sizes

• Color coded by type: red=executable, blue=text,green=image, yellow=program, gray=unknown

• What can we see?

Blue and green patterns are web pages (www site)

Image repository for PhotoMesa

Gray rectangle is a bug, temporary files taking 10% of the www space

Two similar patterns = two versions of the mathlab system

Techniques

• Use accelerated graphics with OpenGL• 2GHz Pentium4• 1600x1200 pixels resolution• Now off-the-shelf!

• Push existing visualization techniques to their limits• Space filling (treemaps)• Overlapping (scatter plots)

Relying onAccelerated Graphics

• Balance the CPU/GPU work

• GPU can perform many operations “for free”• Geometric transformations• Color transformations• Color interpolation• Translucency• Counting overlaps

CPU prepares data and sends it to GPU

• Bottleneck is communication

CPU

GPU

Screen

Relying onAccelerated Graphics

• Breaks the 106 barrier• 1 million items at interactive speed

• Permits use of animation• E.g. for understanding view transitions

• But requires:• optimizing algorithms• using unusual programming techniques• adapting visualization techniques

Example of Adapted Visualization Techniques

• No rectangle outlines• Spares pixels• Avoids sending the

geometry twice

• Color shading• Separate similar items• “Free” with

accelerated graphics cards

Animated Transitions 

Dynamic Labeling

Conclusion

• You can now break the 106 barrier!• Was limited to 104 • E.g. can visualize the phylogenic tree of species

• Still technically limited by graphics hardware, but close to the perceptual limits• New IBM screen with 10 million pixels

• Need more work to understand how humans can make sense of this amount of data

• Send your 106 data sets!

Credits

• Thanks to HCIL for inviting me and providing the rich environment for this work

• Thanks to Catherine Plaisant, Ben Shneiderman and Ben Bederson for their help and advice

• www.cs.umd.edu/hcil/millionvis