Three 20th century "revolutions" in American geography'

During the 20th century, the evolution of American geography went through three major periods of change. The first period of change, which began in the 1920s and extended through the 1930s, initially consisted of a move away from environmental determinism toward "man-land" relations; then a move from man-land relations to an emphasis on regional study, or areal differentiation. The second change period, from the early 1950s to the late 1960s, saw a shift away from areal differentiation toward spatial analysis, involving quantitative methods and the application of theory. The third period began in the early 1970s and has extended beyond the 1980s. The period was marked by a stress on social theory and a strong rejection of the work in spatial analysis. The three periods of change are compared in terms of six selected characteristics: (1) type of change; (2) pace of change; (3) intensity of debate accompanying change; (4) operational characteristics of change; (5) impact of change; and (6) disciplinary and societal context of change. An overview of the periods of change suggests three possible interpretations: monotonicity, periodicity, and continuity.