He observed the migration data between 1885 and 1889 and arrived at certain very important conclusions which may be taken as the laws of migration.
Subsequently, other leading scholars like Lee corroborated his findings and added some new laws of migration. The laws of migration, advocated by Ravenstein, are as under:
(i) The Majority of Migrants go Only a Short Distance (Distance Decay Law):
This law seems to have been operational at least since the medieval times and is still operative today. With the advent of modern transportation, the average distance travelled by migrants may have increased, but relatively short moves are still the most common.
For example, the first major concentrations of the American black (Negroes) population in northern cities were in Baltimore, Washington and Philadelphia, all of which are relatively close to the source areas of migrants who left the south in large numbers after 1910.
There is a tendency that most of the migrants move short distances whereas few go long distances. This tendency is known as distance decay.
This expression applies to most of human activities. In fact, there is a decline in the amount of some phenomena with increasing distance from a focal place.
In other words, many human activities and features tend to cluster near accessible places, so their frequency, volume or value usually declines with distance from the point of attraction.
This tendency applies to the land values around a market, population densities ranging an urban centre, number of migrants to a place of attraction, and numerous other phenomena that are affected by spatial interaction.
As an example, consider the number of migrants to city X who came from districts A-G. When the amounts of migration are plotted on a vertical axis and the corresponding distances are displayed on the horizontal axis, the graphed trend indicates that migration declines (i.e., ‘decays’) as distance increases.
(ii) Migration Proceeds Step by Step:
Ravenstein’s second law of migration is that the inhabitants of the country (rural area) immediately surrounding a town of rapid growth flock into it; the gaps thus left in the rural population are filled up by migrants from more remote districts (rural areas), until the attractive (gravitation) force of one of our rapidly growing cities makes its influence felt, step by step, to the most remote corner of the region.
Accordingly, sequential moves extend the effects of migration spatially such a series of moves was an important feature of migration to the American frontier in the 19th century when farmers who wanted to move on to new lands would often sell out to later migrants.
On a different scale, a series of step by step residential shifts is usually generated in urban areas today when a family moves into a newly built house and thus vacates an older house, which is then reoccupied by another family (which leaves another residential gap and so on).
(iii) Migrants Going Long Distances generally go by Preference to One of the Great Centers of Commerce or Industry:
This tendency of moving towards the great centers of commerce and industry has been operative since medieval times, when London attracted population from all parts of England. The pull of large cities is apparent in the developing countries.
The industrial and commercial centers of Tokyo, Mumbai, Kolkata, Delhi, Karachi, Lagos, Sao Paulo, New York, Manila, Jakarta, Seoul, Shanghai, Mexico, Rio de Jeneiro, Djakarta, Bangkok, Tehran, Cairo, Dhaka and Nairobi, Hyderabad, Bangalore, Ahmadabad, Kanpur and Pune.
The effect of a large place on the size of the migration field is expressed by a Gravity Model. This mathematical model states that the number of migrants to a place is directly related to the population size of that place but inversely related to the migratory distance.
(iv) Each Current of Migration Produces a Counter-current of Lesser Strength:
This law of migration seems to be universal and applicable in almost all the developed and developing countries.
Even in the extreme case of slave trade (15th-19th centuries) produced a tiny counter flow back to Africa of people who, in one way or another, were able to regain their freedom and to return to their homes. Migrants who choose to move long distances to new places often move back.
For example, of the 13 million migrants to the United States from 1900 to 1914, an estimated four million returned to Europe during the same period.
In recent years, the proportion of emigrants from the United States has increased relative to the number of immigrants into the country, with the largest numbers returning to Mexico, Germany, Canada and the United Kingdom.
(v) The Natives of Towns are Less Migratory than those of Rural Areas:
This observation was related to a stage of economic development in Europe in the 19th century when rural-to-urban migration was predominant. In most of the developed and developing countries today, movement is still mainly from rural to urban places.
At present time, most of the developed countries have large urban majorities and relatively small rural populations. Therefore, most migration is inter-urban or intra-urban (within a city). In these developed countries, there is an increasing trend of outflow from urban centers to rural areas.
This migration is associated with the decentralization of Industrial jobs and the willingness of commuters (daily passengers) to travel long distances to their urban places of work.
(vi) Females Migrate more Frequently than Males within the Country of Birth, but Males Frequently Venture Beyond:
This law of migration was related partly to a stage of economic development and partly to its particular cultural context. Since women had few employment opportunities in rural areas, they tended to migrate to cities.
At present, the gender of the majority of migrants depends on cultural conditions as well as on economic and employment opportunities. In India, for example, many more males migrate from rural areas to cities than do females.
During the British period, Calcutta (now Kolkata) and Bombay (now Mumbai) were the main centers of commerce, trade and industries and attracted the people from distant places of Bihar and Uttar Pradesh.
Nowadays, all the million cities of India, particularly Mumbai, Delhi, Kolkata, Chennai, Hyderabad, Ahmadabad, etc., are attracting male migrants from all corners of the country. Migration between rural Indian villages, however, is commonly made by females because brides traditionally move at the time of marriage to the village of bridegrooms.
Man is more active in international migration than woman. In the Gulf countries and Saudi Arabia, there are large number of immigrants from India, Pakistan, Bangladesh, Sri Lanka, Indonesia, Philippines and South Korea and over 85 per cent of them are male workers.
(vii) Most Migrants are Adults; Families rarely migrate out of their Country of Birth:
This law contains two observations. The observation concerning adults is universal and indisputable. In voluntary migrations, the majority of people are adults.
The second part of the law is more problematic. It is certainly true that families find it more difficult to move than unmarried adults, but owing to the cultural, religious and political factors, families migrated from one country to another country.
Many refugees migrated from India to Pakistan and Pakistan to India in 1947 and from Bangladesh to India in 1971.
Similarly, families migrated from Ireland to Canada; from Uganda and Kenya to UK and USA; from Somalia and Ethiopia to Yemen, Egypt and Saudi Arabia; and from Palestine (west bank of Jordan and Gaza Strip) to Syria, Lebnon, Libya, Kuwait and Saudi Arabia.
(viii) Large Towns grow more by Migration than by Natural Increase:
Universally accepted that large cities grow faster because of migrants and population influx for example, over 60 per cent of the total population of Delhi, Mumbai and Kolkata belongs to people who came into these cities from the distant parts of the country in search of employment and got settled.
Most of the large towns and cities in the developing countries today are growing very rapidly by the immigration of people from the rural areas.
In addition to job opportunities which have always attracted migrants to large cities), today’s major cities of the developing countries offer more medical/ educational facilities and social entertainment
(ix) The Main Causes of Migration are Economic:
This law is also universally accepted. It has been argued that international migrants tend to be influenced more by conditions in the area of destination than by the pressure of population at home.
The movement of Indian labourers to Saudi Arabia and the Gulf countries is mainly because of unemployment in rural India and better job opportunities in the South-West Asian countries.
It is, however, difficult to verify that the major reason for migration is economic. Human motivation, decisions and behavior are so complex that it is very difficult to compare the relative importance of economic factors with other considerations.
For example, moving at the time of marriage is not regarded as primarily an economic move in those societies having love marriages.
Also many persons with wealth or large pensions enjoy the flexibility of choosing their residence in areas having an attractive physical and/or social environment.
Most of the above discussed laws of migration, advocated by Ravenstein, are universally accepted. There are, however, many questions which Ravenstein did not address.
For example, the non-economic, cultural, social, political, psychological and religious causes of migration have not been examined by him. Since the time of Ravenstein, several other theories and generalizations have been propounded by other scholars to explain the process of migration.