S4 SUPPLEMENT 2

us to compare consumption of coal and natural

gas during the same period.

Questions

1. In what year was the gap between coal use
   and natural gas use the widest? In what year
   was it narrowest? Describe the trend in coal
   use since 1995.


2. Compare Figures 1 and 2. Among trends in
   oil, coal, and natural gas use, which one grew
   the most sharply between 1950 and 1980?
   Likewise, we can compare many variables
   on the same scales. Figure 3 depicts U.S. energy
   consumption for six different energy resources
   between 1980 and 2007 and projections to


3. It uses scales to measure time on the
   x-axis and energy consumption in quadrillions
   of British thermal units (a standard unit of
   energy required to produce a certain amount of
   heat) on the y-axis.

go through the same process in reverse to fi nd a

year in which oil consumption was at a certain

point.

Questions

1. What was the total amount of oil consumed
   in the world in 1990?


2. In about what year between 1950 and
   2000 did oil consumption first start
   declining?


3. About how much oil was consumed in 2007?
   Roughly how many times more oil was con-
   sumed in 2007 than in 1970? How many
   times more oil was consumed in 2007 than
   in 1950?
   Line graphs have several important uses.
   One of the most common applications is to
   compare two or more variables. For example,
   while Figure 1 shows worldwide oil consump-
   tion over a certain time period, Figure 2 enables

Graphs and Maps are Important
Visual Tools

A graph is a tool for conveying information that
can be summarized numerically by illustrating
the information in a visual format. This informa-
tion, called data, is collected in experiments, sur-
veys, historical studies, and other information-
gathering activities. Graphing can be a powerful
tool for summarizing and conveying complex
information, especially in the ever-expanding
fi elds of environmental science.
In this textbook and accompanying web-
based Active Graphing exercises, we use three
major types of graphs: line graphs, bar graphs,
and pie graphs. Here you will explore each of
these types of graphs and learn how to read
them. In the web-based Active Graphing exer-
cises, you can try your hand at creating some
graphs.
Another important visual tool that can
serve the same purpose of communicating
complex information is a map. Maps can be
used to summarize data that vary over small
or large areas—from ecosystems to the bio-
sphere, and from backyards to continents. We
discuss some aspects of reading maps relating
to environmental science at the end of this
supplement.

Line Graphs

Line graphs usually represent data that fall
in some sort of sequence, such as a series of
measurements over time or distance. In most
such cases, units of time or distance lie on the
horizontal x-axis. The possible measurements of
some quantity or variable, such as temperature
that changes over time or distance, usually lie
on the vertical y-axis. In Figure 1, the x-axis
shows the years between 1950 and 2010, and
the y-axis displays the possible values for the
annual amounts of oil consumed worldwide in
millions of tons, ranging from 0 to 4,000 million
(or 4 billion) tons. Usually, the y-axis appears on
the left end of the x-axis, although y-axes can
appear on the right end, in the middle, or on
both ends of the x-axis.
The line on a line graph, sometimes referred
to as the curve, represents the measurements
taken at certain time or distance intervals. In
Figure 1, the line represents changes in oil con-
sumption between 1950 and 2007. To fi nd the oil
consumption for any year, fi nd that year on the
x-axis (a point called the abscissa) and run a verti-
cal line from the axis to the consumption line.
At the point where your line intersects the con-
sumption line, run a horizontal line to the y-axis.
The value at that point on the y-axis, called the
ordinate, is the amount you are seeking. You can

SUPPLEMENT

2 Reading Graphs and Maps (All Chapters)

Oil consumption

(million tons)

Year

0

1000

2000

3000

4000

Line summarizing data

1950 1960 1970 1980 1990 2000 2010

Y-axis

Abscissa X-axis

Ordinate

Consumption

(million tons of oil equivalent)

Year

0

500

1000

1500

2000

2500

3000

3500

1950 1960 1970

Coal

Natural gas

1980 1990 2000 2010

Figure 1 World oil consump-

tion, 1950–2007. (Data from U.S.

Energy Information Administra-

tion, British Petroleum, Interna-

tional Energy Agency, and United

Nations)

Figure 2 World coal and natural

gas consumption, 1950–2007.

(Data from U.S. Energy Information

Administration, British Petroleum,

International Energy Agency, and

United Nations)