Читать книгу Geography For Dummies - Jerry T. Mitchell - Страница 112

Area symbols use gray tones or colors to depict phenomena that characterize areas as opposed to points or lines and are separated into two basic varieties:

 Nominal symbols identify qualitative characteristics or phenomena that pertain to areas or regions. Figure 5-6, for example, uses nominal symbols to identify official languages of South American countries.

 Choropleth maps (from the Greek choros and pleth, meaning place and value respectively) use colors or gray tones to show how the quantity or numerical value of something varies from one area to the next. Figure 5-7 uses gray tones to depict population density in South American countries. Choropleth maps always process data, and do not map raw numbers. These maps always show data per something else. Cows per square mile. Income per capita. Doing so removes the influence that the area size has on the data representation. For example, wouldn’t you expect Texas to have a lot of tornadoes simply because Texas has so much land area? More informative is how many tornadoes that state has per square mile, say to Florida, for direct comparison purposes.

(© John Wiley & Sons Inc.)

FIGURE 5-6: This map uses nominal area symbols to identify the distribution of Primary European Languages of South America.

(© John Wiley & Sons Inc.)

FIGURE 5-7: This choropleth map uses shades of gray to show population density in South America.