On the impact of spatial momentum

Momentum, the population growth that occurs after a fall in fertility to replacement level, has long been appreciated as a factor in the future population growth of many countries. This paper argues that another aspect of growing populations—their high proportion rural—is also a potential source of significant growth, referring to the additional growth attributable to geographical redistribution as spatial momentum. Using simplifying assumptions, a model for analyzing spatial momentum is developed based on population composition, rates of growth, and levels of interregional migration. Calculations are then done using (i) hypothetical populations exhibiting a range of plausible demographic behavior, and (ii) the population of Mexico, 1970. The results show that spatial momentum can have a substantial impact on ultimate population size under commonly encountered circumstances. 1 Department of Sociology, Pennsylvania State University, University Park PA 16802, USA. Email: [email protected] Demographic Research Volume 6, Article 3 http://www.demographic-research.org 50