COLOR is a complex subject and can be studied in many different ways.

Physicists, chemists,
physiologists, psychologists, philosophers, musicians, writers, architects, and artists approach color from
different perspectives, with distinct purposes. The physicist looks at the electromagnetic spectrum of
energy and how it relates to color production. Chemists examine the physical and molecular structures
of colorants, the elements in substances that cause color through reflection or absorption. The
physiologist treats the mechanisms of color reception by the eye-brain pathway, and the psychologist
deals with the meaning of color to human beings. Finally, the artist works with aesthetic qualities of
color, using information gained from the physiologist and psychologist.

Color in thematic mapping is perhaps the most fascinating and least understood of the design elements.
Color is subjective rather than objective. . On the one hand, color pro- vides so many design options that
designers often quickly seize the opportunity to include it. Yet the inclusion of color invites many
potential problems. Two individuals may view the same color but perceive it differently. Computer
monitors attempt to produce the same color but generate colors with slight variations because they
have various settings, such as video card resolution, color calibration, and the ambient light conditions
that may impact the color displayed. The paper map printed in color will appear different when printed
on a color laser jet printer than the way it appears on an ink jet printer. The quality of the paper on
which the map is printed can also have an impact on the way the color is perceived by different users.
Color is also affected by the ambient light conditions in which the map is viewed. In sum, the designer
can never be totally certain as to how the reader(s) will respond to the color in a map. However, if
allowed to choose, most map designers choose color mapping because of its inherent advantage of
greater design freedom.

Another problem in dealing with color is that it is difficult, if not impossible, to set color rules. Certain
standards for color use have been adopted for some forms of mapping, notably on topographic maps
but No standards or rules for color use, except for a few conventions, exist for thematic maps.

LIGHT AND THE COLOR SPECTRUM

Light is that part of the electromagnetic energy spectrum (EMS) that is visible to the human eye,, fig a.
This radiation spectrum is characterized by energy generated by the sun descending on us at different
wavelengths. These wavelengths vary from very short (10—12 cm) to very long (105 cm, or 1 km). All
visible light comprises a very small portion of this spectrum and varies from 400 nm (nanometers—a
billionth of a meter, or 10—9 meters) to about 700 nm. The composite of all visible light wavelengths is
referred to as white light and is colorless. Color, however, is simply light energy at different places along
this visible light portion of the electro- magnetic spectrum. When our eyes detect light energy at
approximately 750 nm in wavelength, we see red; when we detect wavelengths at 350 nm, we see
violet. We see light that is either emitted by a source or reflected from an object. The sun is, of course,
the source of the EMS and the source of visible light. Similarly, incandescent light fixtures, computer
monitors, television screens, and other electronic devices also emit energy in the visible light portion of
the spectrum. We see this light directly and we interpret the images and colors generated by that
energy. However, we also see images based upon reflected energy. Reflected light bounces off objects
and is somewhat modified by the process of reflecting. The colors that we see from printed maps result
from light reflecting off of the pa- per and the printed ink forming the map image. Some of the ambient
light is absorbed by the paper and ink and thus we see the wavelengths that remain after that
absorption. The fact that we can see light either by direct emission from a computer monitor or
indirectly from light reflected from a surface creates a problem for the cartographer in design and use.
Virtual maps displayed on-screen use color models that are different from color printed maps. As with
all map design, the cartographer must consider the means of presentation when selecting map colors.

COLOR PERCEPTION

Reading thematic maps is a process involving the eyes and brain of the map reader. Light emitted by the
computer monitor or reflected off the map is sensed by the eyes, which report sensations to the brain,
where cognitive processes begin. The sensing and cognitive processing of color is called color
perception. The human eyes [cornea, iris, lens, retina, rod cells, cone cells, optic nerve] are wondrous
organs, often considered to be external linkages to the brain itself.

Color blindness is a facet of color perception that affects about eight percent of males and less than one
percent of females. This is usually a hereditary condition, although not always. The manifestation is that
the subject can see only blues and yellows and may have difficulty in perceiving distinctions between
reds and greens and some yellows.

Physical Properties of Color

The generation of color will occur in either illuminant mode or reflective mode. The illuminant mode
requires a light source and the eye-brain sensing system of the viewer while the reflective mode, also
known as the object mode, requires three elements: a light source, an object, and the eye-brain system
of the viewer. The illuminant mode applies to virtual maps generated for viewing on-screen with the
computer monitor generating the energy for image dis- play. The reflective mode occurs when a map is
printed and the light striking the map reflects back to the eye of the map reader. For printed maps the
physical characteristics of color are also affected by the quality of the object’s surface. Some surfaces
permit all light to pass through them, such as acetate film or laminate. These are called transparent
objects. Most objects are reflective of portions of the visible spectrum; that part of the spectrum that is
reflected defines the color of the surface. Surfaces that absorb all light are opaque and appear black.
The amount of light that is reflected from surfaces can be plotted on a diagram that is called a spectral
reflectance curve. Surfaces without ink appear white, assuming that the printed medium is white

SPECTRAL REFLECTANCE (R) CURVES OF SEVERAL COLORED MATERIALS; Notice that white reflects the
most light and black the least. Also, the similarity in the curves of colors close to each other (red and
yellow or blue and green) is quite remarkable
COLOR THEORIES

Depending on the whether the map is viewed on-screen or printed, two prominent color theories apply:
additive color theory and subtractive color theory. The former specifically applies to light generated in
the illuminant mode when color images are viewed on-screen, and the latter applies to the reflected
mode.

Additive Color Theory

Red, green, and blue are called the additive primary colors because they can, in various combinations,
produce any other hue in the visible part of the energy spectrum. We consider white light to be made up
of three primary colors—red, green, and blue (RGB) — because these cannot be made from
combinations of other colors. Viewed individually we see the single color; however, when combined we
can generate any number of other colors. In that area where all three colors overlap, we will see white;
whereas in those areas where two colors overlap, we will see magenta, cyan, or yellow. Colors produced
by computer monitors, television screens, or movie film are the result of additive primaries of emitted
light.

ADDITIVE AND SUBTRACTIVE COLOR MODELS In the additive color model (a), red, green, and blue are the
primary colors. Combining two additive primary colors produces magenta, cyan, or yellow. The
combination of all three additive primaries produces white. In the subtractive color model (b), magenta,
cyan, and yellow are the primary colors. Combining two subtractive primary colors (in printed form)
produces red, green, or blue. The combination of all three subtractive primaries produces black.

Subtractive Color Theory

Color produced by printing is not based on the additive primaries of emitted light but on inks or
pigments laid down on paper. These inks reduce the wavelength of the energy being reflected, thus
subtracting the energy being absorbed by the ink and reflecting the remaining energy. For example, red
ink absorbs the blues and greens and reflects the red to the reader’s eye.
 Additive Primaries Subtractive Primaries

Red + Green =Yellow Magenta + Yellow = Red

Red + Blue = Magenta Magenta + Cyan = Blue
Green + Blue = Cyan Cyan + Yellow = Green Red
+ Blue + Green Magenta +Yellow + Cyan

Absence of color = White Absence of color = Black

COLOR MIXING USING ADDITIVE AND SUBTRACTIVE PRIMARIES

COMPONENTS OF COLOR

Hue

Hue is the name we give to various colors: the reds, greens, blues, browns, red-oranges, and the like.
Each hue has its own wavelength in the visible spectrum. Now, although hues and their relationships to
other hues may be illustrated in many ways, a customary way, especially by the artist, is on a color
wheel.

A 12-PART COLOR WHEEL, SHOWING APPROXIMATE WAVELENGTHS OF THE VARIOUS HUES; Color
wheels are typically used by artists but can be useful in describing certain color associations (such as
complementary colors and opposites). Typical color wheels often contain 8 or 12 hues.

The color wheel has been used extensively in the discussion of color. This refraction is the same that we
observe in a rainbow. Color on the wheel is sequential according to the wavelength in the visible
spectrum. We normally think of the color sequence of red, orange, yellow, green, blue, indigo, and
violet, which is conceptualized by the mnemonic device of a fictitious person, Roy G. Biv. Theoretically, a
color wheel can contain an almost infinite number of hues, but most include no more than 24. Eight or
12 are more common, 12 being especially useful for artists. The organization of hue on the color wheel
is not based on the physical relationships of the hues but is simply a conventional way of showing visual
hue relationships. Although the color wheel normally contains 12 hues, the human eye can theoretically
distinguish millions of different colors. In ordinary situations, however, we are not called on to do so; in
cartographic design, our assortment of hues is certainly far less. In fact, it would be difficult to imagine
any case where a map reader would have to identify more than a dozen (this is common on land-use or
geologic maps).

Saturation

Saturation is also called chroma, intensity, or purity. This color dimension can be thought of as the
vividness of a color and can best be understood by comparing a color to a neutral gray. With the
addition of more and more pigment of a color, it will begin to appear less and less gray, finally achieving
a full saturation or brilliance. For any given hue, saturation varies from zero percent (neutral gray) to
100 percent (maximum color). At the maximum level, the color is fully saturated and contains no gray.
You might think of it as “watering down” a color. Starting with the strongest color (saturated), we can
add water and the color becomes weaker or less pure (unsaturated).

Value

Value is the quality of lightness or darkness of achromatic shades and chromatic colors. Conceptually
easy to grasp, value can be thought of as a sequence of steps from lighter to darker displays of gray. The
lowest value, specified as zero, will produce a light neutral gray, and 100 percent gray will produce
black. Chromatically progressing up the value scale, the hue becomes successively darker. This provides
us with shades of a particular color—for example, dark red compared to light red. It is this increase in
value that cartographically presents increments of a hue in the design of choropleth maps.

Sensitivity to value is easily influenced by environment, and apparent lightness or darkness is not
proportional to the reflected light of achromatic surfaces. A given gray, or hue of a specified value, looks
one way when examined individually against a white background but differs when viewed in an array of
colors on a computer monitor. This concept applies to both emitted and reflected light. In art, value is
con- trolled by the addition of white or black pigment to a hue. If white is added to a hue, a tint results.
When black is added a shade is produced. A tone results from adding amounts of a hue, white, and
black.

COLOR MODELS

In the various GIS, mapping, and artistic software, color is selected based upon a particular color model.
The model is named using the key letters of the models components these include HSV, HSB, HSL, RGB,
and CIE

HSV

This model refers to the components of color described above: hue, saturation, and value. This model
may be visualized as an inverted cone (or hexacone) with the upper surface resembling the color wheel,,
Around the circumference of the conical disc, color hues are arranged in wavelength sequence
beginning with red, as the circle’s origin, and progressing around the 360-degree space with the
remaining hues. Thus, hues are distributed such that complementary colors are 180 degrees apart. Most
observers are able to differentiate approximately 150 steps around the disc. Saturation is indicated as a
position from the cone’s axis, a saturation reference number of zero percent (or gray), progressing
incrementally to the outer rim of the disc where a reference number of 100 per- cent is found.
Movement outward from the axis increases the level of saturation of the color. The color value is
distributed vertically along the cone’s axis. At the tip of the cone, a value of zero percent indicates black.
You can increment up the axis, increasing the value until you reach the top of the conical disc or a value
of 100 percent, indicating white.

HSV COLOR MODEL CONE; Hue is distributed along the 360° of the color wheel. Hue is identified by its
angular position, in degrees, beginning with red at zero degrees. Value is achieved along the vertical axis
of the cone, and saturation increases outward from the axis.

RGB

The color model is visualized using a RGB color cube,, The cube has black as its origin with three axes
radiating outward at 90°. Each axis represents one of the three color primaries. Numerically, each
primary is specified in steps of 256 increments ranging from 0 to 255. A value of 255 represents the
maximum amount of illumination intensity or saturation of color. This is because computer software
specifies color steps using 8-bit color. That is, each of the three components is specified using a binary
equivalent of 28. The resultant effect of the 256 steps in each color component is that a computer
display is capable of producing over 16 million colors. GIS, mapping, and artistic software also provide a
similar color mixer for selecting color using the RGB model.
RGB AND CMY COLOR CUBES; the cube represents a visualization of the way in which the color primaries
are combined. The RGB model (a) has values ranging from 0 to 255 along each color axis. The CMY
model (b) has values that increment by percent from 0 to 100.

CMYK

The primary model for printed maps is that of the subtractive primary colors of CMY (cyan, magenta,
yellow). Each primary is specified according to percentage increments between 0 and 100. The
combination of 100 percent of all three primaries produces the color black. The absence of these
primaries produces white (although, in reality, the absence of the primaries results in the color of the
paper). Potentially, the various combinations of one-percent increments can generate one million
colors. However, in the printed medium too many other variables come into play which limit the
number of colors you can reliably create. Such variables include the paper quality and color of the paper,
purity of the printer ink, and ambient light conditions of the viewing mode. The quality of the paper can
determine the receptivity of ink and thus impact the density of the ink being applied. The color of the
pa- per has the potential of affecting the perceived color by the map user as it too provides absorption
capabilities, thus reducing the wavelengths of light reflecting off its surface. The purity of the printer’s
ink can also impact the perceived color. In theory, the combination of the three primaries at maximum
density will produce black. However, as a consequence of variable ink purity the resultant color when
printing these colors over the top of each other may be a dark gray.
Grayscale

The grayscale uses an achromatic approach to presenting differences in shades of black. It is most
applicably used for maps to be photocopied or printed in black and white on a laser printer or printing
press. One should limit the number of grayscale levels to five or six on a given map. Beyond that, the
ability of the map user to differentiate between gray levels is diminished. If you know that the map is to
be produced in an achromatic manner, select the gray- scale as your color model before beginning your
map design. Conversion from a color model, especially an additive model, to grayscale is not always as
successful in creating different gray levels as actually beginning your design with that model.

SUBJECTIVE REACTIONS TO COLOR

Color Preferences

Warm colors are those of the longer wavelengths (red, orange, and yellow), and cool colors, at the
opposite end of the spectrum, have shorter wavelengths (violet, blue, and green). Children about the
age of four or five years prefer warm colors. Red is most popular, with blues and greens next. Young
children also prefer highly saturated colors,

Some children’s color choices

1. As children are aware only of small ranges in hue, colors should be chosen from within the basic
spectrum colors—blue, green, yellow, orange, and red.

2. Because school-age children begin to reject fully saturated colors, a step or two down the
saturation range is more desirable.

3. Children appear to dislike dull unattractive colors, so color choice should avoid these. Stay close
to the spectral hues

4. Children generally reject achromatic color schemes— the gray scale. These reduce the
attractiveness of the map.

5. Choosing colors that have greater compatibility with what is expected yields greater
comprehension. Thus, for example, blue is better than red for water

As we mature and leave childhood, our color preferences change. Generally, we tend to favor colors at
the shorter wavelengths. The greenish-yellow hues are the least liked by both men and women. Women
show a slight preference for red over blue and yellow over orange, whereas men slightly prefer blue
over red and orange over yellow. Both sexes choose saturated colors over unsaturated ones. Most color
experts would agree that other variables, such as color environment, product name, packaging, con-
text, and merchandising schemes, are also important in color choice

Colors in Combination

General guidelines include

1. The most pleasant combinations result from large differences in lightness. Lightness (or value)
contrast is necessary in pleasant object-background combinations.

2. A good background color must be either light or dark; being intermediate in lightness makes it
poor.

3. Consistently pleasant object colors are hues in the green to blue range, or other hues containing
little gray.

4. Consistently unpleasant object colors are in the yellow to yellowish-green range, or other hues
containing considerable gray.

5. To be pleasant, an object color must stand out from its background color by being definitely
lighter or darker. This is the single most important finding of the study for the cartographer.

6. Vivid colors combined with grayish colors tend to be judged as pleasant.

7. Good and poor combinations are found for all sizes of hue differences (that is, distances apart
on the color wheel).

Connotative Meaning and Color

Connotative responses to colors vary considerably. The literature, both in psychology and advertising, is
sometimes vague and contradictory. Nonetheless, some generalization may be made

The Functions of Color in Design

These can be summarized as;

1. Color functions as a simplifying and clarifying agent. In this regard, color can be useful in the
development of figure and ground organization on the map. Color can unify various map
elements to serve the total organization of the planned communication
 2. Color affects the general perceptibility of the map. Legibility, visual acuity, and clarity (of
distinctiveness and difference) are especially important functional results of the use of color.
3. Color elicits subjective reactions to the map. People respond to color, especially the hue
dimension, with connotative and subjective overtones. Moods can be created with the use
of color.

Further on functions

A summary of the functions of color in cartographic applications would include:

1. To establish figure-ground organization

2. To establish a visual hierarchy

3. To develop a balance in the map

4. To capture the user’s attention

5. To identify and name locations

6. To identify categories

7. To provide emphasis

8. To show order and structure in layout

9. To enhance physical properties of the map

10. To reveal information for better communication

Design Strategies for the Use of Color

Map designers use several strategies [five] to use color to its fullest potential in map communication;

a. Developing Figure and Ground

b. Use of Color Contrast
c. Developing Legibility
d. Color Conventions in Mapping
e. Color Harmony in Map Design

Developing Figure and Ground

The figure and ground organization of the map can be enhanced by the use of color. Color provides
contrast—a necessary component in figure formation. Perceptual grouping by similarity is also
strengthened by the use of color. For example, similar hues are grouped in perception (although they
may in fact be of different wavelengths). On a world map, for example, continents are more easily
grouped as landmasses if they are rendered in similar hues. Colors of similar brightness or dullness are
also grouped, as are warm colors, cool colors, or other like tints and shades. Tints and shades are
grouped with their primary colors. Perceptual grouping of colors is a strong tendency and should be a
positive design element. Generally, warm colors (reds, oranges, and yellows) tend to take on figural
qualities better than cool colors (greens, blues, and purples), which tend to make good grounds. This
may be partially explained by the tendency of the warm colors to advance and the cool colors to recede.

A well-designed map maintains a balance in the placement of components as well as a balance in

aesthetics of the colors selected. The selection of colors used in choropleth or other such quantitative
maps is much less flexible, as the colors will be directly associated with the data which, in turn, is related
to the polygon. its recommend that when selecting colors for quantitative maps you evaluate the
distribution and impact of color and experiment with color ramps that are possibly less vibrant. Color
combinations also affect figure and ground development. Yellow on black is noted to be the most visible
color combination— yellow tends to be perceived as figure. The least visible, and therefore worst
combination move in terms of figure and ground development, is red on green

Figure Colors Ground Colors

Yellow Best Black

White Blue
Black Orange
Black Yellow
Orange Black
Black White
White Red
Red Yellow
Green White
Orange White
Red Worst Green

Use of Color Contrast

Contrast is the most important design element in thematic mapping. Contrast in the employment of
color can lead to clarity, legibility, and better figure-ground development. A map rendered in color with
little contrast is dull and lifeless and does not demand attention. Even in black-and-white mapping (or
one color other than black), contrasts of line, pattern, value, and size are possible. With color, additional
possibilities exist.

Hue contrast can be used in cartographic design as a way to affect clarity and legibility and to generate
different visual hierarchical levels in map structure. Some cartographers believe that hue is the most
interesting dimension in color application in mapping, more so than value or chroma. It is also important
to note that identical hues appear differently, depending on their color environment. Saturation and
value are two contrasts that provide visual interest and, depending on the nature of the map, can carry
quantitative information. Contrast of value is a fundamental necessity in structuring the color map’s
visual field into figures and grounds. Objects that are high in value (relatively light) tend to emerge as
figures, provided other components in the field do not impede figure formation.
Contrast of cold and warm colors can also be used to enhance figure and ground formation on the map.
Artists use this contrast to achieve the impression of distance; faraway objects are rendered in cold
(blue/green) colors and nearby objects in warmer tones. Figures on maps should be rendered in colors
of the warmer wavelengths, relative to the ground hues

Developing Legibility

The legibility of colored objects, especially lettering, is greatly influenced by their colored surroundings.
Symbols in color must be placed on color backgrounds that do not affect their legibility. Black lettering
on yellow (object on background) is a very high legibility combination, and green lettering on red is the
least. The difficulty is exacerbated because the lettering is usually spread over several different
background colors. Black lettering may become illegible as it crosses dull or gray colors. The designer
must pay careful attention to lettering and all color environments in which it is placed.

Color Conventions in Mapping

Conventional uses of color in mapping may be separated into qualitative and quantitative conventions.

Qualitative Conventions. Colors used on maps in a qualitative manner are those applied to lines, areas,
or symbols that show nominal or ordinal information, not amount. Qualitative color conventions use
color hue and saturation to show these nominal (and, in some cases, ordinal) classifications. Many
conventions are quite old—such as showing water areas as blue—and the logic of their use is well
established. Includes

1. Blue for water

2. Red with warm and blue with cool temperature, as in climatic and ocean representations

3. Yellow and tans for dry and little vegetation

4. Brown for land surfaces (representation of uplands and contours)

5. Green for lush and thick vegetation

Quantitative Conventions

When one wishes to make use of the method [graphic] of applying colors in various shades to
geographic maps, he should have regard for the following points:

a. Twelve classes or divisions permit the establishment of a gradation of tints easy to distinguish
from the lightest to the darkest shades and present the further advantage of allowing the comparison to
be limited to six, four, or three classes, when there is a desire to consider only the principal relations.

b. The strongest proportions should be indicated by the darkest shades.

c. When it is a question of showing opposite extremes, the intermediate shades should be omitted
from the scale of colors used.
Color Harmony in Map Design

Color harmony relates to the overall color architecture for the entire map. Harmony includes these
components:

1. Effectiveness of the functional uses of color on the map

2. Appropriateness of the conventional uses of color on the map

3. Overall appropriateness of color selection relative to map content

4. Effective use of the quantitative color plan

5. Effective employment of the relationship of hues

A harmonious design can be judged also on its appropriate use of color convention. Has every care been
taken to provide conventional color wherever possible? Do departures from convention restrict the ease
of communication? Another important component of overall color harmony is the proper selection of
color relative to map content

Any multicolor map has its different colors occupying areas of varying sizes. Color balance is the result of
an artful blending of colors, their dimensions, and their areas so that dominant colors occupying large
areas do not overpower the remainder of the map.

Some guidelines on relationships of harmony include;

1. Most people like pure hues rather than modifications (reds, not purples).

2. Every color should be a good example in its category. If a red is chosen, it should not be possible
to mistake it for a purple. Pure colors, if selected, must be brilliant and saturated.

3. Whites should be white, and blacks should be black.

4. Tints, shades, and tones should be easily seen as such, not confused with pure hues, blacks, or
whites.

5. Colors opposite on the color wheel tend to be harmonious.

6. Harmony can also be achieved by using colors adjacent on the color wheel.

7. Harmony can also be achieved by combining colors of the same hue but with different tints,
shades, and tones
Color schemes

Mapmakers often use variations of hues to create more visually appealing maps. Arrangements or
combinations of colors used for map data are called color schemes, or sometimes color progressions.
Colors that vary in hue are used to show different classes of qualitative data are called categorical color
schemes eg in LULC map. Also progress sions of colors that vary in value and saturation, from light to
dark, are used to show classes of quantitative data on choropleth and dasymetric maps. Sequential color
schemes are used for data values that range from low to high. These color schemes are a light to dark
progression of gray tones or a single color hue. Diverging color schemes are used to show data that has
a critical value in the midrange of the distribution from which other values differ progressively. Colors in
this scheme have variations in two hues that range from light to dark, with a light gray often used for the
midrange class. To help select appropriate colors for their map data, cartographers often rely on the
ColorBrewer app (http://colorbrewer2.org), which guides users through the color scheme selection
process.

Grayscale (top) and single-hue (bottom) sequential color schemes

Diverging color scheme for a map that shows population change