Interactive Information
Visualization of
One Million Items
Jean-Daniel Fekete
University 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?
Two similar patterns
= two versions of
the mathlab system
Gray rectangle is a
bug, temporary files
taking 10% of the
www space
Blue and green
patterns are web
pages (www site)
Image repository for
PhotoMesa
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 on
Accelerated 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 on
Accelerated 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