1. emigration leaving one's homeland to settle in a new place 2. immigration birth rate insufficient to replace the existing population 3. migration resources being used up at a faster rate than they can be replenished 4. overpopulation the movement from one place to another 5. sustainable development the increase in the population of a city 6. underpopulation the number of people exceeds the available natural resources in an area 7. unsustainable development the ability to meet current needs without reducing the ability to meet future needs 8. urbanization the movement of people to a new country