What migration theory holds that migration is concrete, not general?

Lu Yilong, an associate professor of sociology at Renmin University of China, introduced this in his article: E. G. Ravenstein, a British scholar, put forward a theory of population migration in the 19th century. He summarized the laws of population migration in society as follows: 1) Migration is mainly short-distance migration, and long-distance migration is to move to a large industrial and commercial center. Compared with a center that attracts immigrants, the closer the distance is, the more immigrants move in. On the contrary, the farther the distance is, the fewer immigrants move in, and the number of immigrants is inversely proportional to the distance. 2) Migration is often staged. As far as a town is concerned, firstly, people from rural areas around it move in, and then, immigrants from distant rural areas gradually move into rural areas around the town; 3) Migration flow and reverse migration flow coexist at the same time, but the net migration flow usually flows from rural areas to cities. Under normal circumstances, immigrants who migrate to a region also have reverse migration; 4) The female population has certain advantages in short-distance migration; 5) The development of transportation, communication and technology has increased the mobility; 6) Favorable economic factors are the most important factors to attract immigrants.

an American scholar, E.S. Lee, put forward a more detailed model of migration law on the basis of Weinstein's theory. He defined migration as a permanent or semi-permanent change in people's place of residence. He believes that there are four factors related to people's migration and influencing migration: first, factors related to the destination of migration; Second, the factors related to the original residence of migration; Third, it is related to the factors between the migration destination and the original residence, and fourth, it is related to the individual migrants. In the above four aspects, there are positive factors (+) that are conducive to migration, negative factors (-) that are not conducive to migration and neutral factors () that are ineffective. The contest and synthesis of positive and negative factors contribute to the final migration action.

according to this basic principle, Li further proposed that there are some laws of population migration: 1) the scale of population migration varies with the difference between the two places, and the greater the difference in nature, geography and social economy between the two places, the greater the scale of population migration will be. For example, between rural areas and cities, the social structure is quite different, and the migration volume is also relatively large. 2) The scale of migration varies with the structure and characteristics of population groups. Different age, gender and occupational groups have different migration volumes. Large-scale population migration to one direction or destination forms a migration flow. 3) The obstacles in the middle are directly related to the migration. 4) When a large migration flow is formed, it will inevitably produce a reverse migration flow, that is, after a large number of people move out of a certain place, the population from other areas will move in to make compensation. The scale of population migration changes with the change of economic factors. During the period of economic prosperity, the scale of population migration is large, while during the period of economic recession, the amount of population migration is small. 5) Except for special compulsion, the scale and mobility of population migration are increasing with the delay of time. 6) With the different stages of a country's social and economic development, the migration scale and migration rate are also changing.