Visualization

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Visualization

• ENVE/CE 424/524

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Graphic Visualization Components
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Color
Appropriate use of color for data display allows
interrelationships and patterns within data to be
easily observed. The careless use of color will
obscure these patterns. When color is used
'appropriately,' the organization of the
perceptual dimensions of color corresponds to the
logical ordering in the data.
Color has 3 dimensions hue related to a
colors wavelength of electromagnetic
radiation important aesthetically value a
colors lightness or darkness very important
visually - the eye tends to be led by patterns of
light and dark saturation a colors intensity
or brilliance
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Electromagnetic Spectrum
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Common Color Scales
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What colors to use?
General rules of thumb Maps showing a variety
of features can benefit from contrasting
hues Ex soil, geologic, climatic, vegetation,
land us, zoning, Hue differences usually fail
at portraying differences in percentages, rates,
median values, and other intensity measures
because hues have no logical ordering for most
people.
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Limited vs. Complex Number of Hues
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Color Brewer
http//www.personal.psu.edu/faculty/c/a/cab38/Colo
rBrewerBeta.html
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Classification Schemas
Natural breaks classes are defined according to
apparently natural groupings of data values. (GIS
programs that automatically determine classes
usually base them on relatively large jumps in
data values.)
Quantile breaks classes are defined by having an
equal number of observations
Equal interval breaks classes are defined by
uniform intervals
Standard deviation breaks classes are defined by
differences from the mean value.
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Interactive Color Effects
Same color next to light/dark shades shifts the
shade of the perceived color
Different colors next to light/dark shades
shifts the perceived colors to look the same
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Contrast
Color palette is the same in all four images.
Differences in the background color causes our
eyes to perceive brighter or darker colors.
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Two principles for minimizing color damage
1. Pure, bright or very strong colors have loud,
unbearable effects when they stand unrelieved
over large areas adjacent to each other.
Extraordinary effects can be achieved when they
are used sparingly on or between dull background
tones. 2. The placing of light, bright colors
mixed with white next to each other usually
produces unpleasant results, especially if the
colors are used for large areas.
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Violation of Color Principles
Primary home heating fuel by county
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Bathymetric and Elevation Chart
Easy to read
Difficult to read
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Meaningful Spectral (Rainbow) Scale
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White Lies with Maps
A good map tells a multitude of little white
lies, it suppresses truth to help the user see
what needs to be seen. Mark Monier, 1991
An analyst with an agenda can make a map
emphasize or de-emphasize certain aspects of a
story.
Finding the right balance between truthful
storytelling and lying is difficult and requires
accumulated experience.
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Multiple Perspectives
Be cautious when comparing two data sets or two
sets of analyses based on one set of views,
whether it be statistical or graphic. Theres
usually more to the story. Its best to examine
data from both a text/statistical perspective and
a graphical/chart perspective.
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Anscombes Quartet
These four data sets look identical from a
statistical perspective.
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Anscombes Quartet
They dont look anything alike from a graphical
perspective!!
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Statistics vs. Pattern
Two sets of variables with identical
scatterplots, correlation coefficients (r0.93),
and class breaks
Distinctly different map patterns
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Graphical Slight of Hand
Classification set so that patterns are identical
Classification set so that patterns show less
correlation
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Classic Correlation vs. Causality
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What do you see?
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Graphics are subject to viewers preconceptions
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Shaded Relief Map
Calculated using slope and aspect and an
illumination model that uses the sun angle
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Follow the Black Dot
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Multivariate Mapping
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(No Transcript)
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Small Multiples
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Napoleans Russian Campaign - 1812
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Principles of Graphical Excellence
Graphical excellence is the well-designed
presentation of interesting data a matter of
substance, of statistics, and of design.
Graphical excellence consists of complex ideas
communicated with clarity, precision, and
efficiency.
Graphical excellence is that which gives to the
viewer the greatest number of ideas in the
shortest time with the least ink in the smallest
space.
Graphical excellence is nearly always
multivariate.
And graphical excellence requires telling the
truth about the data.
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Intentionally Hidden Lies