High Mobility America's extensive transportation network is an important element in its high level of economic interaction. Goods…

America's extensive transportation network is an important element in its high level of economic interaction. Goods and people move freely within and between regions of the country. Regional interdependence is great; it ismade possible by these interregional flows. Relative isolation is uncommon, but it does exist.
Nearly 20 percent of all Americans change their residence in any one year. Although much of this residential migration is local in nature, it does result in substantial interregional population movement. Until the last decade of the 19th century, there was a strong westward population shift toward frontier agricultural lands. The focus of opportunity then changed and migration shifted to urban areas. More recently, the U.S. economy has entered what some call a post-industrial phase; employment growth is primarily in professions and services rather than primary (extractive) or secondary (manufacturing) sectors. Such employment is much more flexible in its location, and there has been a more rapid growth in such employment in areas that appear to contain greater amenities.