# 20.6 Pie & Area Graphs

## This activity is from the Sourcebook for Teaching Science.

Pie charts (figure 20.20B) illustrate the relative magnitude of a category by the portion of a circle it occupies. Area graphs (figure 20.22B) illustrate the magnitude of change over time. Pie and area charts use the size of the plot, rather than its position, to emphasize key features.

Activity 20.6.1 Pie Charts: Comparing relative magnitude within a data series

Pie charts show only one data series, and are useful when emphasizing a significant element. For example, figure 20.20B shows the leading causes of death in the United States.

(1) What are the causes of death in developing and developed countries? Figures 20.20C and D list the leading causes of death in developed and developing countries according to data collected by the World Health Organization[i]. (Note that the classifications differ from those reported for America by the United States Center for Disease Control[ii] in figure 20.20A.) Construct a pie chart of the 10 leading causes of death in developing countries and compare it with the 10 leading causes of death in developed countries. Describe the differences and offer an explanation for these differences.

(2) Which biomes are most productive? Figure 20.21A lists the approximate percentages of the Earth’s surface that are covered be various biomes and the percentages of the total productivity (amount of biomass produced) accounted for by each biome. Develop pie charts showing the percentage coverage and the percentage productivity such as those shown in figures 20.21B and C. Which biomes have the highest and lowest productivity per unit area? Why is deforestation of the tropical rainforests a global concern?

(3) Sources of energy: The United States and many other developed nations are dependent on foreign sources of energy, particularly oil, to fuel their economies. What percent of America’s energy comes from the burning of fossil fuels (oil, coal, natural gas)? Create a pie chart of American energy consumption from the data in table 20.5. Shade the renewable resources in a different color than the non-renewable resources. What percent of our energy comes from renewable sources (hydroelectric, geothermal, wind, biomass, and solar)

Activity 20.6.2 Area graphs: Illustrating the magnitude of change over time

Area charts emphasize the magnitude of change over time. By displaying the sum of plotted values, an area chart shows the relationship of parts to the whole. Figure 20.22B documents the spread of an infestation of bark beetles on four sides of a mountain over a period of ten months. The graph shows that the spread has been most severe on the south and east slopes.

(1) Seed germination: Area graphs are an excellent tool for plotting experimental data such as that shown in figure 20.23A[iii]. Fifty seeds each of a wild, hybrid, and mutant plant were observed for two weeks after planting. Graph the cumulative seed germination rate using an area graph.

(2) Commercial Satellite launches: The Information Revolution has created a large demand for communications satellites to relay information from one part of the Earth to another. Private companies recognize the potential to make money in this expanding market. Create an area graph of the data in figure 20.23B to show the growth of the commercial satellite business in the early years between 2001 and 2003.

[i] World Health Organization. (2007). Mortality database. Retrieved May 2, 2007 from http://www.who.int.

[ii] National Center for Health Statistics. (2007). Deaths-Leading Causes. Center for Disease Control. Retrieved May 2, 2007 from http://www.cdc.gov.

[iii] National Aeronautics and Space Administration (various dates). NASA Image Exchange. Public domain rocket photographs courtesy of NASA. Retrieved May 1, 2007 from http://nix.larc.nasa.gov.