The article discusses how migration and natural increase impact the growth of cities. By comparing the number of migrants and births minus deaths, researchers can determine which factor contributes more to city growth. The study highlights that the age of migrants and birth rates can affect this balance. The rapid expansion of cities in developing countries raises questions about managing urban growth. Historical examples show how cities have grown in the past. The research aims to understand the role of migration and natural increase in shaping the size of cities.