The movement of large numbers of people to cities is known as

Urbanization

Urbanization refers to the phenomenon where individuals move to cities or towns for various reasons including:

a. More job opportunities

b. More facilities - health, shopping, entertainment, etc.

c. Better technology

Urbanization is increasingly commonly worldwide, in both developed and developing countries. While its benefits include more social growth, modernization and opportunities, urbanization can also lead problems such as: pollution, environmental issues, traffic and in some cases overpopulated cities.