Any area with a large population. Or the land is very unequal, it will cause some pressure on the population to move out of the area. To acquire land to provide sufficient demand .
There are many areas the population or land allocation is not adequate, it will cause a pressure that some people must move out of the area to seek landed more, eating enough. .
any area with a population of more or the allocation of land is not equal, it will cause some pressure on the population to move out of the area to seek land to eat enough to meet the demand for increased