1. Geog 462: Digital Cartography: Graphic Variables
11/27/2018
Geog 462: Lecture 4
GRAPHIC VARIABLES:
SYMBOLS FOR THEMATIC MAPS
Dr. Gregory Elmes

2. 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

3. Geog 462: Digital Cartography
Graphic Variables
Size
Value
Hue
Saturation
Orientation
Shape
Arrangement
Texture
Focus
11/27/2018
Geog 462: Digital Cartography

4. 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

5. Effects of various map projections
Bering Strait?
Antarctica?
South America to Australasia?
(See also Fig 2.06)
11/27/2018
Geog 462: Digital Cartography

6. 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

7. Uses and Abuses of Size and Shape
MacEachren Figs 2.07 to 2.11 p. 21

8. 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

9. 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

10. Visual Variables for Colored Maps

11. 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

12. 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)

13. 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

14. COLOR SATURATION

15. 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

16. 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

17. 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
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Geog 462: Digital Cartography

18. 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

19. WHICH IS THE ‘CORRECT’ DATA MODEL?

20. Visual Representation

21. MATCHING SYMBOLS TO REFERENTS

22. 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