In this article, we begin by reviewing the concept of step migration that originated in E. G. Ravenstein's seminal papers ''The Laws of Migration'' (1885, 1889). As a result of the forces of the Industrial Revolution underway in 19th century Great Britain, migrants moved from farms to villages, from villages to towns, from towns to county seats, and thence to large cities. Throughout much of the industrialization era in the United States, net population movements similarly were upward within the urban hierarchy, and step migration today remains widespread throughout much of the still developing world. Our investigations of recent data and trends, however, suggest that the latest U.S. migration-pattern regime is a strongly contrasting one. Many of the major movements in the system of internal (or domestic) migration are flows down the urban hierarchy, although we note highly differentiated patterns for persons and households at specific stages of the life course. We make use of the newly defined metropolitan and micropolitan Core-Based Statistical Areas (CBSAs) and a seven-level size typology to tabulate origin-destination-specific migration flow data from both Census 2000 and IRS tax-return administrative records for the period 1995-2000. We discuss the causes for net movements being either upward or downward in the national urban hierarchy, including the effects of spatially focused immigration, and movement preferences at various ages, including migration in young adulthood associated with entering and leaving college and the military, as well as moves characteristic of the stages of family formation, childrearing, and retirement.population trends ͉ metropolitan areas ͉ micropolitan areas

Demographic effectiveness, Inward population redistribution, Migration impact, Urban hierarchy,

Almost half a century has passed since Jean Gottmann coined the term “Megalopolis” in reference to the almost continuously urbanized stretch of land spanning the East Coast of the United States from southern New Hampshire to northern Virginia. Because a disproportionate concentration of population resided in this Megalopolis, the northeastern core enjoyed an economic and cultural supremacy, and he termed the Megalopolis “The Main Street of the Nation.” By the later 1960s and 1970s, however, population migration patterns began to reflect the influence exerted by the emergence of a second national core centered on the large metropolitan areas along the Pacific Coast, especially those of the Los Angeles and Bay Area conurbations in California. Although of different character, this burgeoning concentration of population, economic activity, and cultural influence may reflect the development of a West Coast Megalopolis that could soon rival the original Megalopolis of the Northeastern Corridor. Today, the U.S. population distribution is largely a bicoastal one. This article documents the emergence of this bicoastal population distribution. Using historical census data and GIS technology, we present a number of novel ways to graphically portray and examine this population redistribution phenomenon. The United States is not unique in witnessing an increasing share of its inhabitants clustering in coastal zones. Current critical policy concerns about the worldwide vulnerability of coastal populations have focused the need for better coastal population estimates and better mapping methods for portraying population redistribution trends.

No abstract