Difficulty Level One: Why do you think so many big cities in the U.S. are located along major rivers or on the shores of large lakes or oceans?
Answer: Historically, rivers, lake shores and ocean harbors have provided many benefits for cities. These include transportation, commerce (shipping of manufactured goods and natural resources), drinking water (except for cities at seashores), water-power for industry and elecricity, and a means of sewage disposal.

Difficulty Level Two: What percentage of the country's largest 56 cities are located along the banks of large rivers? What percentage are on lake shores? What percentage are on ocean shores? What percentage are not located beside any of these bodies of water?
Answer: 23 cities, or 41%, are on America's largest rivers; 6 cities, or 10% are on the Great Lakes; 12 cities, or 21%, are on ocean shores, and 15 cities, or 28% are on none of these bodies of water.