和遷移的程度成正比的工資差別如圖所示:Mij =βij (Wj – Wi)。 M是移民的數量從地方我將j,β係數表達遷移的障礙,如地方之間的距離和j,數據不足,和政策障礙,可能減少的速度遷移導致調整工資。 β值的增加,當遷移被刪除或減少障礙。 Ravenstein在1989年提出了關於移民的法律Greenwood在1997年提出了這七個法律的概要(1)移民發生在小城市到大城市之間，只要距離不是太大;(2)快速發展的城市吸引了居住在附近農村地區的移民，而這些農村地區勞動力的短缺導致了更多偏遠地區的移民;(3)移民與移民成反比;(4)為了補償大規模的移民潮，第四定律產生了反移民潮(5)向較大城市遷移的移民覆蓋的距離更大;
(6)農村人口比城市人口更容易遷移;(7)與女性相比，男性移民的可能性更小，因為女性更忠於家庭(Chin, A.和Cortes, E. 2015)。 1946年，Zipf給出了國際貿易的引力模型，該模型描述了兩國間跨境貿易的強度。這一理論已被發現在國際經濟學領域有廣泛的用途，因為它提供了經驗關係。城市和區域經濟學家更加強調國內移民領域的消費方法(Clements, K。Dybczak, V。加斯帕,S。索托,m . 2015)。現代國際移民文學可以根據移民動機分為三類。移徙者可以是其服務的提供者、公共物品和便利設施的消費者或商品和服務的生產者。
And the extent of migration is proportional to the wage differential as shown:Mij = βij(Wj – Wi).where M is the number of migrants moving from place i to place j while β is a coefficient expressing the barriers to migration, such as distance between the place i and place j, insufficient data, and policy barriers, that may potentially decrease the speed at which migration leads to adjustment in wages. The value of β increases when the obstacles to migration are removed or decreased.Ravenstein has presented laws for migration Greenwood in the year of 1989 and in 1997 he offered a summary of these seven laws (1)migration takes place from small cities to large cities provided the distance is not too large; (2) rapidly growing cities attract migrants living in nearby rural areas and the shortage of labour in these rural areas leads to migration from more far away locations; (3) emigration and immigration are inversely proportional; (4) to compensatelarge migration wave a counter-wave was produced in the fourth law (5) migrants moving to larger cities cover more distance;
(6) rural population is more susceptible to migrate than the population living in urban areas; and (7) men are less likely to migrate than women as women are more committed to their family (Chin, A. and Cortes, E. 2015).Zipf in 1946 gave Gravity model of international trade that state the intensity of cross border trade between the countries. This theory has been found to be of immense use in the field of international economics as it gives empirical relations. The urban and regional economist laid more emphasis on consumption approach in the sphere of domestic migration (Clements, K., Dybczak, V., Gaspar, S.,&Soto, M. 2015).The modern literature on international migration can be differentiated into three classes depending upon the motive of migration. A migrant can be a provider of his services, a consumer of public goods and amenities or a producer of goods and services.