The Geography of Colorants
The Expanding Use of Color
In the history of maps, color has played many roles, ranging from aesthetic to symbolic. In older maps color was used as decoration, enhancing the illustrations and border, while the actual map was left mostly uncolored. Over time, color expanded into coastlines and political borders and was eventually used to distinguish countries, states and bodies of water.
In antique maps, the colors used were limited by the quality and availability of a few pigments and dyes. While a variety of colorants were used in coloring maps, the most available colorants produced shades of green, red, yellow and blue. It is no coincidence that the most common colors found in basic modern maps echo the colors produced by these pigments - cyan, magenta, yellow and blue. While the colors have stayed somewhat constant, the methods of coloring maps have changed drastically. In older maps, color was added by hand, painted on using watercolor techniques. The results differed from map to map, depending heavily on the skill of the painter. The quality and steadfastness of the colorants available resulted in some color variation even when using the same colorant, as well as changes in color over time. In modern mapmaking, the colors used are synthetic, consistent, and much more stable.
From 1940 to 1960, mapmaking was in transition. Drawing paper was replaced by plastic sheets and mapmaking became a purely photochemical compilation process. During the 1960s, cartography switched from a discipline based on pen and ink to one based almost entirely on computer technology. Traditional draftsmen were replaced by machines, which resulted in a larger scale of map production at a lower cost and guaranteed a certain level of graphic quality and consistency.
In modern mapmaking, color is increasingly used as a method of communicating statistics. A color can represent a number, say a number of people or number of houses, creating a visual map of the population or housing density of an area. Colors are also used to show topography, with different shades representing distances above or below sea level. Different colors are used to communicate types of information, thus a new standard of map coloring has been made. Certain hues of colors are chosen based upon their ability to depict nominal data while other hues are known for better representing ordinal data. For example, red, green, and blue hues might be deemed appropriate for the display of different soil types (a nominal data type) while yellow, orange, and red may be used for highly statistical, or ordinal data. With a wide range of consistent hues and shades available, maps can begin to convey much more than just how to get somewhere.