Data Encoding
Data attributes
• categorical (or ‘nomimal’) – apples, pears, bananas
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– sparrow, goldfinch, robin
• ordered(ordinal)
– small, medium, large
– January, February, March…
• ordered(quantitative) – 10cm, 17cm, 23cm
Stolte, C, and Hanrahan, P. Polaris. IEEE TVCG, 2002 (figures)
Data Marks
• The basic graphical element of an image
• Can be 0D, 1D, 2D, 3D
Visualisation Analysis & Design, T. Munzner, (Ch4)
Channels (Bertin’s “Visual Variables”)
Visualisation Analysis & Design, T. Munzner, (Ch4)
Marks and Channels
channel(s) /variables
used for showing the data
vertical position
vertical position horizontal position
vertical position horizontal position color hue
vertical position horizontal position color hue
size (area)
line/ area
Visualisation Analysis & Design, T. Munzner, (Ch4)
Representing three numbers
Expressiveness principle: choose the channel according to the data attributes Effectiveness principle: encode the most important attributes with the highest ranked channels
Visualisation Analysis & Design, T. Munzner, (Ch4)
Steven’s Psychophysical Power Law (1957)
perception(stimulus) = constant x (strength of stimulus) power
The strength of perceived sensation
is proportional to
the measurement of physical intensity
raised to a power
Perceived sensation is subjective
Physical intensity is objective Visualisation Analysis & Design, T. Munzner, (Ch4)
Channel interference
Visualisation Analysis & Design, T. Munzner, (Ch4)
children, women, men
Scotland, England, Wales, Ireland
number of runners: 10, 50, 100
best race finishing position
Members of a running club
Members of a running club
children, women, men
(nominal, shape)
Scotland, England, Wales, Ireland
(nominal, hue)
number of runners: 10, 50, 100
(ordered & quantitative, area)
best race finishing position
(ordered & quantitative, horizontal position)
Members of a running club
children, women, men
(nominal, shape)
Scotland, England, Wales, Ireland
(nominal, hue)
number of runners: 10, 50, 100
(ordered & quantitative, area)
best race finishing position
(ordered & quantitative, horizontal position)
50 40 30 20 10
Data Encoding
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