Geog 462 Lecture 4 GRAPHIC VARIABLES SYMBOLS FOR

Geog 462: Lecture 4 GRAPHIC VARIABLES: SYMBOLS FOR THEMATIC MAPS 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 12/29/2021 Geog 462: Digital Cartography 2

Graphic Variables • • • Size Value Hue Saturation Orientation 12/29/2021 • • Shape Arrangement Texture Focus Geog 462: Digital Cartography 3

Location in Space • Numerical Level of Measurement – Position in the plane – 2 D / 3 D • Distance – Scale - Ratio Level – Relative - Ordinal Level (Fig 2. 05) • Stereo Model for 3 D - holographic images 12/29/2021 Geog 462: Digital Cartography 4

Effects of various map projections Bering Strait? Antarctica? South America to Australasia? (See also Fig 2. 06) 12/29/2021 Geog 462: Digital Cartography 5

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 12/29/2021 Geog 462: Digital Cartography 6

Uses and Abuses of Size and Shape Mac. Eachren Figs 2. 07 to 2. 11 p. 21 12/29/2021 Geog 462: Digital Cartography 7

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 12/29/2021 Geog 462: Digital Cartography 8

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 12/29/2021 Geog 462: Digital Cartography 9

Visual Variables for Colored Maps 12/29/2021 Geog 462: Digital Cartography 10

Pattern Variation resulting from different color schemes of data in A) B) Value Range C) Spectrally ordered Hue D) Hue range ordered by Value 12/29/2021 Mac. Eachren 2. 14 C p. 24 and plates Geog 462: Digital Fig Cartography 11

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 (Mac. Eachren 1994 p. 25) 12/29/2021 Geog 462: Digital Cartography 12

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 12/29/2021 Geog 462: Digital Cartography 13

COLOR SATURATION 12/29/2021 Geog 462: Digital Cartography 14

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 12/29/2021 Geog 462: Digital Cartography 15

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 12/29/2021 Geog 462: Digital Cartography 16

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 12/29/2021 Geog 462: Digital Cartography 17

Graphic Variables cont • Arrangement – random / regular – Different kinds of things without implying importance – Combine with value for clearer distinction • Orientation – Human vision sensitive • Focus 12/29/2021 Geog 462: Digital Cartography 18

WHICH IS THE ‘CORRECT’ DATA MODEL? 12/29/2021 Geog 462: Digital Cartography 19

Visual Representation 12/29/2021 Geog 462: Digital Cartography 20

MATCHING SYMBOLS TO REFERENTS 12/29/2021 Geog 462: Digital Cartography 21

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 12/29/2021 Geog 462: Digital Cartography 22