This chapter has introduced a set of key concepts that underlie how maps represent data, specifically thematic maps. Mapping as a method to represent data has been related to cartography as a professional field focused on developing the science that supports effective mapping and the practice and technology of generating maps. Emphasis has been on the many different map types, how they are created, and what types of data are best suited for each map type. The core building blocks used to create map symbolization have also been introduced.
To summarize this chapter, maps are abstractions of the real world created through systematic selection, classification, simplification, exaggeration, and symbolization. They are products of the cartographic process, a cyclic process involving data as inputs, the final map as an output, as well as the map maker and map user as the creator and consumer of the map. Thematic maps help reveal geographic patterns that are hard or impossible to find in lists of numbers that data are typically presented in. Graphic variables and color schemes form the building blocks for thematic map construction. Furthermore, different types of thematic maps are used to represent different types of data, both categorical and numerical. Count data, for instance, are conventionally portrayed with symbols that are distinct from the statistical areas they represent, because counts are independent of the sizes of those areas. Rates and densities, on the other hand, are often portrayed as choropleth maps, in which the statistical areas themselves serve as symbols whose color lightness is varied with the magnitude of the attribute data they represent. Attribute data shown on choropleth maps are usually classified. Classification schemes that facilitate comparison of map series, such as the quantiles and equal intervals schemes demonstrated in this lesson, are the most common.
Try This: The Good, The Bad, and The Ugly
Surf the Internet and find a good map, a bad map, and an ugly map. What attributes are the important ones for assigning each map to the category you put it in?