This document discusses different types of population movements that impact cities like Birmingham in the UK. It defines the processes of urbanization, suburbanization, counter-urbanization, and re-urbanization and provides examples of each in Birmingham. It also examines reasons for national and international migration such as retirement, jobs, education, worker shortages, EU migration, and war. National migration within the UK can impact Birmingham's age structure, ethnicity, housing, and services as people move to the area for different reasons over time.