Visualizing Environmental Science

Graphing Appendix 469

Some bar graphs are constructed so that their bars
run horizontally instead of vertically (Figure A.7). Note
that in contrast to Figure A.6, in this case the x-axis por-
trays the numeric variable (population percentage) and
the y-axis portrays the categorical variable (discrete age
ranges). Also note that bars extend from their central
value of zero on the x-axis to the right to display the nu-
meric values for females, and to the left to display the
numeric values for males. In this horizontal orientation,
the numeric value of each bar is determined by its length
rather than its height. By ex-
amining this graph we can in-
fer that Ethiopia’s population
is likely to keep growing rap-
idly because the majority of its
males and females are in the
younger, pre-reproductive age
categories.
A pie chart shows the pro-
portion of some total value
taken up by two or more differ-
ent categories. Each category is
graphically portrayed as a “slice”
of the total (the entire “pie”),
and the size of each of these slic-
es corresponds to its proportion

0

2

4

6

8

Per capita ecological

footprint (hectares/person)

India France United

States

10

Based on data from World Wildlife Fund,

Living Planet

Report, 2008.

Male Female

Bars run

horizontally

Rapid growth:

Ethiopia

Age

100+

75–79

80–84

85–89

90–94

95–99

70–74

65–69

60–64

55–59

50–54

45–49

40–44

35–39

30–34

25–29

20–24

15–19

10–14

5–9

0–4

Central value

10

Percentage of population

8 6 4 2 0 2 4 6 8 10

Based on data from Population Reference Bureau.

A bar graph is often used when one variable is a num-
ber and the other variable is a category. For example,
the bar graph below shows how a numeric variable (per
capita ecological footprint) varies across a categorical vari-
able (country). In such cases the height of each bar rep-
resents the numeric value for each category. Thus in this
case (Figure A.6) we can see that the per capita ecological
footprint in the United States is more than twice as great
as France’s and more than five times greater than India’s.

of the whole. In the pie chart below (Figure A.8), we can

readily see from the size of the different slices that the

mining industry generates over three-quarters of the to-

tal amount of solid waste we produce, and that less than

2 percent of this waste comes from municipal sources. By

examining the second pie chart that illustrates the pro-

portional contribution of the different materials within

the municipal solid waste slice, we can also see that pa-

per and paperboard make up almost a third of the entire

municipal waste category.

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Figure A.7

Mining

76%

Agriculture

13%

Municipal

solid waste

1.5%

a. Composition of Total Solid Waste, 2010

Industry

9.5%

b. Composition of Municipal Solid Waste, 2010

Food

waste

13.9%

Plastics

12.4%

Metals

9.0%

Glass

Wood 4.6%

6.4%

Rubber,

leather and

textiles

8.4%

Other

3.4%

Paper and

paperboard

28.5%

Yard

waste

13.4%

Based on data from United States Environmental Protection Agency (EPA), 2010. Based on data from United States Environmental Protection Agency (EPA), 2010.

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