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Geog 462: Digital Cartography: Graphic Variables
11/27/2018 Geog 462: Lecture 4 GRAPHIC VARIABLES: SYMBOLS FOR THEMATIC MAPS Dr. Gregory Elmes
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Geog 462: Digital Cartography
GRAPHIC VARIABLES Exploration - Presentation Continuum Visual Logic / Visual Contrast Noticing the unexpected / Conveying the message Building on Bertin’s typology of graphic variables Fundamental units - building blocks 11/27/2018 Geog 462: Digital Cartography
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Geog 462: Digital Cartography
Graphic Variables Size Value Hue Saturation Orientation Shape Arrangement Texture Focus 11/27/2018 Geog 462: Digital Cartography
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Geog 462: Digital Cartography
Location in Space Numerical Level of Measurement Position in the plane 2D / 3D Distance Scale - Ratio Level Relative - Ordinal Level (Fig 2.05) Stereo Model for 3D - holographic images 11/27/2018 Geog 462: Digital Cartography
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Effects of various map projections
Bering Strait? Antarctica? South America to Australasia? (See also Fig 2.06) 11/27/2018 Geog 462: Digital Cartography
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Geog 462: Digital Cartography
SIZE and SHAPE SIZE Ordinal level - change symbol size Easily distinguished by eye Small, Medium, Large Low, Moderate, High SHAPE Nominal level - different kinds of things Human vision not sensitive to small shapes ‘Reading’ versus ‘Seeing’ maps 11/27/2018 Geog 462: Digital Cartography
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Uses and Abuses of Size and Shape
MacEachren Figs 2.07 to 2.11 p. 21
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Geog 462: Digital Cartography
COLOR VALUE Variation in lightness or darkness High values light (white, yellow) Low values dark (navy blue, black) % Black [0% - 100%] Human perception of brightness does not correspond in linear way with measured reflectance Value has order - ordinal data Quantitative - Magnitudes of values BUT human vision does not distinguish between many gray tones 11/27/2018 Geog 462: Digital Cartography
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Geog 462: Digital Cartography
COLOR HUE Red, blue , green sensation Measure of wavelengths that surface reflects or emits Electromagnetic spectrum Hue differences and representation of ordered or numerical data No everyone knows the order Hue values overwhelm perception 11/27/2018 Geog 462: Digital Cartography
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Visual Variables for Colored Maps
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Pattern Variation resulting from different color schemes of data in A)
B) Value Range C) Spectrally ordered Hue D) Hue range ordered by Value MacEachren Fig 2.14 C p.24 and plates
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Combining Hue and Value:
The highest Value hue of the spectrum (Yellow) occupies the middle of the range. Hues decrease in value in both directions. A) Yellow through green to blue or violet B) Yellow through orange to red (MacEachren 1994 p. 25)
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Geog 462: Digital Cartography
Color Saturation Purity of the Hue Defined only in color context Obvious visual order The range of wavelengths reflected / emitted from a specific location on the map Narrow range - Pure hue Wide range - impure or muddy color 11/27/2018 Geog 462: Digital Cartography
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COLOR SATURATION
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See Mersey (1990) for the experiment and results
Color Schemes a) Unordered Hue b) Two Hue Progression c) Spectral Hues d) Hue-Value Series e) PMS-Value Series f) B&W Value Series See Mersey (1990) for the experiment and results
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Sequential Color Schemes
SAME HUE A) Lightness varies (color value) B) Lightness and Saturation Vary DIFFERING HUES A) Portion of Color Circle B) Entire Color Circle
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Graphic Variables cont.
Texture Spatial frequency of pattern components Human vision highly sensitive to texture Large area to be readily visible Depth perception Coarse texture nearer viewer, fine texture father away VISUAL SEPARATION 11/27/2018 Geog 462: Digital Cartography
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Graphic Variables cont
Arrangement random / regular Different kinds of things without implying importance Combine with value for clearer distinction Orientation Human vision sensitive Focus 11/27/2018 Geog 462: Digital Cartography
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WHICH IS THE ‘CORRECT’ DATA MODEL?
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Visual Representation
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MATCHING SYMBOLS TO REFERENTS
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Geog 462: Digital Cartography
POINTS TO REMEMBER MAPS REFER TO A REALITY (Usually) BUILDING BLOCKS FOR REPRESENTATION Spatial Dimension Level of Measurement Visual Variables CHOOSING THE APPROPRIATE DATA MODEL FOR THE REALITY, or the phenomenon you wish to depict 11/27/2018 Geog 462: Digital Cartography
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