When migrants leave an area, they also arrive at another area. To truly comprehend the growth in population of a city or country you need to subtract the number of migrants that move into a country, from the number of migrants that move out.
In the image you see a supermarket.
In a supermarket food is constantly being sold, while new products are coming in. To find the profit of the supermarket you need to subtract the number of foods being bought from the number of food products being sold.

The second law is that most of those who migrate, move a short distance rather than a long one. An example of this can be seen in the picture. The fresh vegetables are sold in farmers markets. These farmers markets get their vegetables from local farms because they are a shorter distance and easier to get than say a farm in California. Similarly migration over a shorter distance is easier and shorter than migration from a larger distance.

As you can see migration is occurring more frequently in the US internally than externally.

The third law states that it is more likely for people to migrate to a big city rather than a rural area or smaller place. You find this trend because people move due to betterment of opportunities, and bigger cities offer better opportunities than say a smaller town in the middle of nowhere. In this picture you see New York. New York is a staple city in which people move to because they can gain better opportunities. This is also why New York has a larger population than Coppell.

As seen in the graph the three largest cities in the US are really well known, and have the largest populations.

In many studies, research shows that most people move because of economic opportunities. Many big cities and urbanized areas have more jobs than rural areas. So people from the rural areas tend to move to the larger cities where there are more jobs and better jobs.

The picture shows the city of Surat which is ranked 4th in the world of growing urbanized cities. Because of this the city has much more job availability than rural parts of India, and is why Surat is seeing an increase of population.

As seen in the picture, Surat has gone from having the least in population to having a population of more than 4.5 million people. This growth in urbanization is also why Surat is ranked at 8 in the top 10 populated cities in India.

The fifth law states that adults are more likely to move than families. This occurs because young adults move in order to give their families a new and better place to start. You tend not to see as many families move because when an adult moves they have to provide for themselves which is hard as it is, but with a family it makes matters harder to take care of everyone in the family.

An example of this is when you see international college students moving from places like Asia, India, and Europe to the US.