Region
United States
11
Arctic regions
6
Tropics
4
Antarctica
2
Balkan Peninsula
2
Mediterranean Region
2
Polar regions
2
Africa
1
Africa, North
1
Alaska
1
Arctic Ocean
1
Asia
1
Asia, Central
1
Brazil
1
California
1
Developing countries
1
Europe
1
Europe, Eastern
1
Four Corners Region
1
Great Lakes (North America)
1
Great Lakes Region (North America)
1
Greece
1
Middle Atlantic States
1
Middle East
1
Netherlands
1
New England
1
North America
1
North Slope
1
Québec (Province)
1
Rio Grande Watershed (Colo.-Mexico and Tex.)
1
San Francisco
1
South Asia
1
West (U.S.)
1