The physical features of the land have shaped population in the Americas in very significant ways. This influence has waned to some degree with improvements in transportation technology, but the effect is still very significant.
Particularly in colonial times, there was little in the way of ground transportation. The most efficient way to move people and goods was over water. This meant that the presence of water was a very significant factor in determining where there would be large populations of people. In the United States, the largest cities have always been on water. New York City is on the ocean and on two rivers. Chicago is on Lake Michigan which, of course, connects to the other Great Lakes. Cities in the interior, such as Pittsburgh, were typically sited on rivers as well.
Conversely, there has been relatively low population density in places that have other sorts of physical features. Mountain ranges, for example, do not tend to have large cities. Neither do deserts.
It is true that technology has mitigated this impact. Highways and railroads have caused rivers and lakes to be less important. However, population patterns are still affected by the physical features of the Americas.