Gravity model of migration
Encyclopedia
The gravity model of migration is a model in urban geography
derived from Newton's law of gravity
, and used to predict the degree of interaction between two places (Rodrigue et al. 2009, 216). Newton's law states that: "Any two bodies attract one another with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them."
When used geographically, the words 'bodies' and 'masses' are replaced by 'locations' and 'importance' respectively, where importance can be measured in terms of population numbers, gross domestic product, or another appropriate variables. The gravity model of migration is therefore based upon the idea that as the importance of one or both of the location increases, there will also be an increase in movement between them. The farther apart the two locations are, however, the movement between them will be less. This phenomenon is known as distance decay
.
The gravity model can be used to estimate:
The gravity model can also be used to determine the sphere of influence of each central place by estimating where the breaking point between the two settlements will be. An example of this is the point at which customers find it preferable, because of distance, time and expense considerations, to travel to one center rather than the other.
The gravity model was expanded by William J. Reilly in 1931 into Reilly's law of retail gravitation
to calculate the breaking point between two places where customers will be drawn to one or another of two competing commercial centers.
Opponents of the gravity model explain that it can not be confirmed scientifically, that it's only based on observation. They also state that the gravity model is an unfair method of predicting movement because its biased toward historic ties and toward the largest population centers. Thus, it can be used to perpetuate the status quo.
Urban geography
Urban geography is the study of areas which have a high concentration of buildings and infrastructure. These are areas where the majority of economic activities are in the secondary sector and tertiary sectors...
derived from Newton's law of gravity
Newton's law of universal gravitation
Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them...
, and used to predict the degree of interaction between two places (Rodrigue et al. 2009, 216). Newton's law states that: "Any two bodies attract one another with a force that is proportional to the product of their masses and inversely proportional to the square of the distance between them."
When used geographically, the words 'bodies' and 'masses' are replaced by 'locations' and 'importance' respectively, where importance can be measured in terms of population numbers, gross domestic product, or another appropriate variables. The gravity model of migration is therefore based upon the idea that as the importance of one or both of the location increases, there will also be an increase in movement between them. The farther apart the two locations are, however, the movement between them will be less. This phenomenon is known as distance decay
Distance decay
Distance decay is a geographical term which describes the effect of distance on cultural or spatial interactions. The distance decay effect states that the interaction between two locales declines as the distance between them increases...
.
The gravity model can be used to estimate:
- Traffic flowTraffic flowTraffic flow, in mathematics and civil engineering, is the study of interactions between vehicles, drivers, and infrastructure , with the aim of understanding and developing an optimal road network with efficient movement of traffic and minimal traffic congestion problems.-History:Attempts to...
- Migration between two areas
- The number of people likely to use one central place
The gravity model can also be used to determine the sphere of influence of each central place by estimating where the breaking point between the two settlements will be. An example of this is the point at which customers find it preferable, because of distance, time and expense considerations, to travel to one center rather than the other.
The gravity model was expanded by William J. Reilly in 1931 into Reilly's law of retail gravitation
Reilly's law of retail gravitation
In economics, Reilly's law of retail gravitation states that larger cities will have larger spheres of influence than smaller ones, meaning people travel farther to reach a larger city....
to calculate the breaking point between two places where customers will be drawn to one or another of two competing commercial centers.
Opponents of the gravity model explain that it can not be confirmed scientifically, that it's only based on observation. They also state that the gravity model is an unfair method of predicting movement because its biased toward historic ties and toward the largest population centers. Thus, it can be used to perpetuate the status quo.
See also
- Gravity model of tradeGravity model of tradeThe gravity model of trade in international economics, similar to other gravity models in social science, predicts bilateral trade flows based on the economic sizes of and distance between two units. The model was first used by Tinbergen in 1962...
- uses the same approach for modelling trade flows between two locations, also discusses variants of the initial gravity model