Gravity model of Migration

The gravity model of migration was developed by William J. Reilly in 1931 based on the newton gravitational force. It predicts the movement of people, goods, services knowledge, technology, and capital between two places. 
Newton Gravitational force=G*m1*m2/r^2



The gravitational force of migration:

Pf =P1*P2/r^2

Where Pf is the migration force of attraction.
P1=population of place 1
P2=Population of place 2
r=distance between two place





Basic assumptions:


  • Should have uniforms topography
  • There should not be a human-made barrier

Major variables:
  • Distance
  • Population size


As per Gravity model of Migration:
  • Larger the cities larger the attraction of people, goods, knowledge, talents, and capital than the smaller place.
  • Migration is inversely proportional to distance. Smaller the distance more migration.

Supporting examples:
  • Larger interaction between Delhi and Mumbai as compare to Delhi & Lucknow and Mumbai & Lucknow.
  • Large "in migration" can be noticed in Mumbai as compared to Lucknow.
Opposing examples:
  • Migration between India and China is very less as compared to between India and USA despite the following facts:
    • India population; 134 Crore
    • China population: 140 crore
    • USA population: 33 crore
    • Distance between India and China: approx 3,000 km.
    • Distance between India and the USA: 13500 KM.

Criticism of the gravity model:
  • Technological advancement in the transport sector is not taken into consideration.
  • Connectivity is the deciding factor of migration, not the distance.
  • The number of opportunities is the deciding factor of the migration rather than population size and distance between the cities.

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