Free Online Course on World Geography, Weather, Climate & Regions
Figure 4.6.1, United States' population in
the year 2000. (National Atlas of the United States, 2007.
http://www.nationalatlas.gov/natlas/Natlasstart.asp)
Figure 4.6.2, United
States' average annual precipitation. (“Precipitation Map of the
United States,” National Atlas of the United States, 2005.
http://nationalatlas.gov/printable/precipitation.html#list)