All maps are abstractions and simplifications of the real world. Certain real-world phenomena are selected by the cartographer, represented by symbols on the map, and presented to the map reader who interprets the map and learns something about the selected phenomena in their geographic setting. . . It is important . . . to recognize the perceptual limitations that are common to all map readers, and to design the map to accommodate those limitations.
(Thematic Maps, Their Design and Production (1982) David Cuff & Mark Mattson London: Methuen & Company)
To make a map, one must go through the following steps of cartographic communication:
Please read the following from Goode's World Atlas [Edward Espenshade ed. Rand McNally 1988] and, for more detailed information and examples, read the hyperlinks to the University of Texas Cartographic Communication website.
Simplification involves omitting details that will clutter the map and confuse the reader. The degree of simplification depends on the purpose and scale of the map. If the cartographer is creating a detailed map of Canada and merely wants to show the location of the United States, he or she can draw a simplified outline of the country. However, if the map requires a precise identification of the states in New England and the Great Lakes region, the mapmaker will have to draw a more detailed outline, still being careful not to distract the reader from the main features of the Canadian map.What is the goal of the map?
Classification of data is a way of reducing the information to a form that can be easily presented on a map. For example, portraying precise urban populations in the United States would require using as many different symbols as there are cities. Instead, the cartographer groups cities into population categories and assigns a distinct symbol to each one. With the help of a legend, the reader can easily decode the classifications. Issues of Statistical Generalization
Symbolization of information depends largely on the nature of the original data. Information can be nominal (showing differences in kind, such as land versus water, grassland versus forest); or ordinal (showing relative differences in quantities as well as kind, such as major versus minor ore deposits); or interval (degrees of temperature, inches of rainfall) or ratio (population densities), both expressing quantitative details about the data being mapped.
Cartographers use various shapes, colors, or patterns to symbolize these categories of data, and the particular nature of the information being communicated often determines how it is symbolized. Population density, for example, can be shown by the use of small dots or different intensities of color However, if nominal data is being portrayed-for instance, the desert and fertile areas of Egypt-the mapmaker may want to use a different method of symbolizing the data, perhaps pattern symbols. The color, size, and style of type used for the different elements on a map are also important to symbolization."
Don't forget to include full citations and a bibliography to tell me where you got your information.
More Helpful links:
Mapping Data - Examples of symbolization side by side
What Is a Good Map?
Elements found on virtually all maps
Cartographic Communication - U. of Texas, Austin
Cartography and Understanding Maps - Matt Rosenberg
Color Use Guidelines - Cynthia A. Brewer