Note #11:Color Use in Thematic Maps

Color Use in Thematic Maps
Spectral Color
• Chromatic: with color
• Achromatic: white, gray, or black
• Color is a perceptual processing of electromagnetic radiation by our eyes.
• Only a tiny portion (400-700 nm) of EM spectrum can be perceived: violet, blue, …, red.
Three Psychological Dimensions of Color
1) Hue
• Hue is the name we give to the various colors: red, green, blue, brown, etc.
• Each hue has its own wavelength in the visible spectrum
2) Brightness and Value
• The quality of lightness or darkness of achromatic and chromatic colors;
• Value is controlled by the addition of white or black pigment to a hue;
3) Chroma (saturation)
• Brilliance, richness, and purity of color;
• With the addition of more and more pigment of a color, it will appear more and more
• Chroma varies from 0 percent (gray) to 100 percent (saturated, pure color, and contains
no gray);
• Achromatic colors have 0 chroma.
Color wheel:
• Typically used by artists to illustrate the hues and their relationships to other hues;
• A color wheel include no more than 24 hues, and 8 or 12 are the more common;
• Complementary colors are opposite on the color wheel. Mixing two complementary hues
produces gray. The primary complementaries are yellow-violet, blue orange, and redgreen.
Warm and Cold Colors
• Warmer colors are those of the longer wavelengths, red, orange, and yellow;
• Cool colors, at the opposite end of the spectrum, have shorter wavelengths; violet, blue,
and green.
• Warm and cool are psychological definitions of these color range.
Advancing and Retreating of Colors
• Warm colors with the longer wavelengths (red) appear closer to the viewer when seen
along with a color of shorter wavelength. Cool colors appears far away or deeper to the
• High values of colors advance, and low values recede;
• Deep and highly saturated colors advance, and less saturated colors recede;
• Advancing colors should be applied to figural objects to develop figure-ground on maps.
Colors in combination
• Lightness (value) contrast is necessary in pleasant figure-ground combinations.
• A good background color must be either light or dark
• To be pleasant, the object color must stand out from its background color by being
definitely lighter or darker.
• Vivid colors combined with grayish colors tend to be judged as pleasant.
Connotative Meaning of Color
• Connotative meanings of colors are subjective;
• Yellow-cheerfulness; strong yellow-warning; red-blood, fire, danger; blue-coldness; deep
blue-silence; orange-harvest; white-cleanliness, etc.
Color Specification Systems
1. Munsell Color System
• Use three color dimensions: hue, value, saturation;
• Ten hues make up the color band, and ten number divisions are associated with each hue.
There are 100 different hues on the color wheel.
• Vertical axis is the value. The top of value scale is 10 (white), the bottom is 0 (black),
and the middle is 5 (gray).
• Saturation is represented by steps going outward from the value axis for each hue band.
• Used in the US.
2. Ostwald Color System (Natural Color System)
• The color wheel is composed of 24 separate hues, and 3 in each of 8 primary hues;
• Value and saturation variation of hue is achieved by mixing different amounts of white
and black to each hue;
• If white is added to a hue, a tint results. When black is added, a shade is produced. When
equal amounts of a hue, white, and black are added, a tone results.
• Compatible to printers, artists, ink manufacturers;
• Commonly used in Europe.
Computer Color Models
1. RGB Color Model:
• Most applicable to the color generated by computer display devices
• Based on additive mixture of three primary color: red, green, and blue;
• Each hue is specified in terms of intensities of red, green, and blue. At the corners of
RGB color cube are:
• Equal amounts of RGB give grays along a scale from black (0, 0, 0 for RGB) to white
(255, 255, 255 for RGB). The line joining the black and white points in color space is the
neutral or gray axis.
• The combination of different values (256x256x256) of RGB creates 16,777,216 possible
colors on the computer display.
2. HLS (HVS) Color Model
• Many color graphics programs specify color based on hue, lightness (value), and
• Hue is given as an angle counter-clockwise between 0 and 360, lightness (value) is given
an integer between 0 (black) and 100 (white), and saturation between 0 (neutral gray) and
100 (pure color).
3. CMYK Color Model
• Subtractive color combination of Magenta, Cyan, Yellow, and Black.
• Process color printing uses the transparent inks (pigments): Magenta, Cyan, and Yellow,
which together can create any hue in a continuous-tone color image. MCY are the
subtractive primary colors. Magenta subtracts (absorbs) the blues and greens and
transmit red light.
• Theoretically, mixing magenta, cyan, and yellow should produce pure black, but it results
in a dark muddy brown in practice. Black is usually used to overcome this limitation.
• Color printer or plotters use this model to produce the color images, known as four-color
process printing. Color produced by printing is not based on the additive primaries of
projective light, but on inks or pigments laid down paper.
Opponent Process Theory
• Our perception of color is based on a lightness-darkness channel and two opponent color
channels: red-green and blue-yellow.
• We see no hues as mixtures of red and green, or of yellow and blue.
• All color are mixtures of any two non-opponent primary hues: blue+green=cyan, green +
yellow=yellow-green, yellow+red= orange, red_blue=magenta.
• Important for selecting appropriate color schemes for balanced and bipolar data.
• Two color schemes spacing the sides of the diagram are successful for unipolar data: a
yellow-red sequence and a green-yellow sequence, both of which involve hue and
lightness changes.
Design Strategies For the Use of Color
• Warm colors tend to take on figural qualities, and cool colors tend to make good grounds.
• Far-away objects are rendered in cold colors and nearby objects in warmer tones
• Yellow on black is noted to be the most visible color combination, and yellow tends to
be perceived as figure. The least visible and therefore worst combination is red on green
in terms of figure-ground development.
• Black lettering on yellow is the most legible, and green lettering on red is the least.
• A balance of complementary colors can achieve harmony and stability in a map
• The use adjacent colors on the color wheel can also achieve hormony.
Color Conventions for Qualitative Maps
• On maps of nominal data classes, different hues should be used to show qualitative
• The maximum number of hues is often limited between 8 and 15.
• Blue for water
Red with warm and blue with cool temperature in climatic and ocean representations;
Yellow and tans for dry and little vegetation
Brown for soil or bare ground (uplands and contours)
Green for lush and thick vegetation
Color Convention for Quantitative Maps
• The quantitative color plan is based on graded series of colors to show varying amounts.
Either color value (lightness) or chroma differences correspond with numerical
gradations in the mapped variable.
• A number of color schemes can be used for quantitative maps, namely, the schemes to
use the color dimensions of hue, value, and chroma to symbolize varying amounts of data
on the map.
Color Schemes (Plan)
1. Value Progression Scheme
• On achromatic maps, a value progression from white to black, or from light to dark gray.
2. Single-Hue Progression Scheme
• Sequential schemes
• Color value decreases and chroma increase systematically as the colors grade from white
to the pure hue;
• Increasing amount of a single ink is applied to areas represents greater data values.
• Producing steps of gray or monochromatic color sequence, e.g., white to red single hue
3. Bi-Polar (Double-ended) Progression Scheme
• Diverging color schemes
• Used when a mapped variable ranging from negative to positive, below or above zero, or
bad to good.
• Dark red at the positive end may grade to light red, to white, to light blue, and to dark
4. Complementary Hue Progression Scheme
• An ordered mixing of complementary hues, e.g., blue and yellow are complementary
hues, and colors in this sequence will grade from both complementary hues toward gray
in the center of the progression. Diverging color scheme
5. Part-spectral Hue Progression Scheme
• Use adjacent hues of part of the color wheel to show variations in amount. For example,
blue-green-yellow, or red-orange-yellow.
• Colors grading between two adjacent opponent process hues, such as yellow and red, will
depict the magnitude variation while emphasizing the degree of mixture.
6. Blended Hue Progression Scheme
• A progress of related hues, one or more of which is not part of the spectrum.
• A very popular blended hue progression used to show elevation differences is from
yellow through orange to brown.
7. Full-spectral Progression Scheme
• Use full spectral hues from blue through red to symbolize quantitative data on the map
• Most commonly used to portray successive elevations on relief maps: water-blue,
lowlands-green, intermediate elevations-yellow, highlands-reddish