Zipf's Inverse Distance Law

Introduction:

G.K Zipf, a well known geographer developed the gravity hypothesis of migration based on Ravenstein laws of migration ;most of the migrants are from short distance and igration proceeds step-by-step. It is also known as (P1 X P2)D hypothesis or social physics of Newton.It is used to predict the interaction between two places.This law is based Newtons Gravitational Law which states that gravitational force between two bodies is directly proportional to the product of their masses and

inversely proportional to the distance between them.This model can be use to explain :

1.      Traffic Flow

2.      Migration between two areas

3.      The number of people likely to use one central place.

Statement of the Law:

There is an inverse relationship between the numbers of people moving and the distance moved. The volume of migration between the two places, (mainly place of origin and place of destination) is directly proportional to the size of two places and inversely proportional to the distance between the places.

Mathematically:

Iij=k . Pi.Pj/Dij

Where, Iij=Volume of migration from i to j

            Pi and Pj=Size of place i and j in-terms of area, population, socio-economic  setting                     

            Dij=Distance between i and J

              K=a constant

            

Explanation of the Figure:

•      The gravity is the force of attraction of earth pulls an object towards its center or surface. In this hypothesis, the gravity is symbolized to show the forces that pull the people towards the place of destination.In this model, according to Zipf, people will migrate even if they are not pushed from their place of origin, they migrate because they are pulled by better socio-economic future at the some other place (destination). In the gravity, earth pulls any objects towards it surface, in a similar way ; people are pulled towards the big cities by its pull effect (same as gravity) not by push effect at the place of origin.  This attraction force is determined by the size of destination in-terms of socio-economic facilities, size of population and distance between place of origin and destination. In this model, the pull factors are treated as ‘attracting mass’ and while the mass pull , the distance acts as friction to migration.