Map Design, Color
and Visualization

James S. Aber

Table of Contents
Nature of color Use of color
Visualization References


It could be said that without good grammar, spelling and structure, this text could not be interpreted by you, the reader. Likewise, a map with poor design does not depict appropriate visual information to the viewer. Good graphic design consists of many aspects, which can be summarized as a "pleasing appearance" that is easy to interpret without visual clutter or confusion. Size, shape, color, symbols, title, legend, borders and other graphic or text elements each contributes to the overall effect a map has on the viewer. The best GIS database may be a failure, if it cannot be displayed effectively. In contrast, a mundane GIS database may be highly regarded, if its display is dramatic. Never underestimate the importance of map design for the key goal of GIS--conveying geographic information to other users.

Nature of color

Stereoscopic color vision is the most important human sense (Drury 1987). The nature of color and human perception of color are, thus, key elements in cartography. A great deal of research has been done on the use and effectiveness of color in map display.

The visible spectrum of colors. Image obtained from the Canadian Centre for Remote Sensing--see CCRS.

The primary colors--blue, green, and red--are also called additive colors, because they can be added together to create all visible colors of the spectrum. Subtractive colors (complementary colors) are created by removing (subtracting) an additive color from white light.

Color printing and film are based on subtractive colors, whereas the human eye and video display and digital photography are based on additive colors.

In printing a color document from a computer display, the printer must translate additive colors into corresponding combinations of subtractive colors. Table prepared by the author.

The Munsell color code is the internationally accepted standard for describing color quantitatively. It is based on three attributes: value, hue, and chroma--see soil color.

Color can be described also with the color cube, in which the x,y and z axes represent red, green, and blue color intensitities--see color models.

Color intensity (saturation) is usually given in byte-binary (0-255) or hexadecimal (base-16, 00-FF) numbers. See examples to left; table prepared by the author.

Use of color for maps

The use of color on maps is much more than simply a way to construct a legend. Color carries visual meaning, it directs attention, it can emphasize or obscure features. Thus, color selection is an important element of map design. The human eye can distinguish tens of 1000s of different colors, but only 20-30 gray tones. The eye is also superbly able to identify patterns and boundaries (edges) and to detect movement.

The standard VGA color monitor can display 16 colors from a total color selection of 262,144 (64³). Super VGA monitors can display up to 256 simultaneous colors from a total of several million possibilities. More advanced monitors can display still more colors. On a static map, however, the eye cannot relibly match more than 16-20 simple colors from the legend with the map. This limited ability can be expanded by the addition of pattern elements (symbols) to the basic colors. Still, there is a practical limit to how many colors should be displayed on a map. Maps are easiest to interpret when the number of colors does not exceed 10 to 12. Too many colors (>20) creates a map that is visually cluttered.

Color may carry standardized meanings in particular applications. Common physiographic maps are a good example: blue = water bodies, green = vegetation, brown = desert/mountains, white = ice or snow, etc. A standard color scheme is often used on geological maps: green = Cretaceous, yellow = Quaternary, etc. Such color schemes are often varied to suit the local circumstances.

Generalized geologic map of Kansas, which follows a standard color scheme for rocks of different ages. Taken from KGS.

The sequence of colors in a legend serves an important function in showing the visual relationship of map features. A smooth sequence of colors is best for showing data that are continuously variable, for example a topographic surface. A group of similar colors could be used to designate subclasses of a major class. Dissimilar colors create visual barriers between features that are not related to each other.

Generalized elevation map of Kansas, in which color classes show continuous gradation from blue (low) to brown (high). Taken from KansasGIS.

Colors may be thought of as "cool" or "hot" according to wavelength. This general distinction is useful in deciding how to employ various colors on a map.

Cool and hot colors induce a color stereoscopic effect--cool colors appear farther away, hot colors appear closer. This effect can be used to create a pseudo depth perception in maps, for example topographic maps of elevation (Eyton 1990). The effect can be enhanced by using black boundaries between color areas, a small contour interval, and bright high-saturation or fluorescent colors.

Digital elevation model of Hutchinson East 1:250K quadrangle. Elevations are shown with a color-stereoscopic scale--cool colors are low and hot colors are high. The red areas are drainage divides in the Flint Hills upland of east-central Kansas. Image processing by J.S. Aber.

Visualization in GIS

Cartography is the art of visual display for human interpretation of graphical representations or scale models of the Earth's surface. For GIS, users fall into three groups in terms of their likely visualization needs and experiences (Davies and Medyckyj-Scott 1994).

  1. Hands-on users -- scientists and technicians relatively experienced in handling GIS databases and creating displays.

  2. GIS audience -- viewers of finished products--teachers, students, bureaucrats, administrators, elected officials, and the general public.

  3. GIS designers -- cartographers and computer engineers who design software and hardware systems for GIS.

GIS allows interactive visual display in ways that are not possible with conventional paper maps. Aside from area and perimeter measurements, there are few ways in which a user can interact with a paper map. Modifying the legend, symbols or colors is impossible, as are any statistical or spatial queries. Paper maps are analyzed almost completely by "looking" at the map and making mental interpretations of features. GIS visualization adds many aspects that are not possible with paper maps (Davies and Medyckyj-Scott 1994).

References

Map schedule.
ES 551 © J.S. Aber (2008).