Population Studies is the broader aspect of demography. It combines both formal and substantive demography. Formal demography is the study of human population in relation to changes in their sizes, structures and spatial distribution as a result of the interplay between three demographic processes, fertility mortality and migration. Substantive demography provides tools to examine the interactions of demographic, social, economic, and environmental, political and cultural processes on which the entire human population operates. Population studies cover development planning and policy issues as they relate to human population.