How is migration a determinant factor of population change?

In India, most migrations have been from rural to urban areas because of the “push” factor in rural areas. These are adverse conditions of poverty and unemployment in the rural areas and the “pull” of the city in terms of increased employment opportunities and better living conditions. Migration is an important determinant of population change. It changes not only the population size but also the population composition of urban and rural populations in terms of age and sex composition. In India, the rural-urban migration has resulted in a steady increase in the percentage of the population in cities and towns. The urban population had increased from 17.29 percent of the total population in 1951 to 27.78 percent in 2001. There has been a significant increase in the number of ‘million-plus cities’ from 23 to 35 in just one decade i.e. 1991 to 2001.