Gravity Model- The Gravity Model predicts that the number of the optimal location of a service is directly related to the number of people in the area and inversely related to the distance people must travel to access it. This means that a business or service will have more interaction with people in a highly populated area, and the farther away that business or service is from a population, the less interaction it will have. A specific example would be Wal-Mart. A Wal-Mart in Atlanta, Georgia would get more interaction than a Wal-Mart in Columbia, South Carolina would because Atlanta as a higher population. If that same Wal-Mart in Georgia was moved to a smaller city that was farther away, then its interaction would decline because less people live in the smaller area and the people in Atlanta would not travel that far to interact with Wal-Mart.
Central Place Model- The Central Place Model explains the distribution of services, based on the fact that settlements serve as centers of market areas for services; larger settlements are fewer and farther apart than smaller settlements and provide services for a larger number of people who are willing to travel farther. The theory was created by Walter Christaller who was a German geographer. He came to the conclusion that people gathered in cities to share goods and ideas that exist solely for economic purposes. Christaller made three main assumptions. 1.) Humans will always purchase goods from the closest place that offers the good, 2) Whenever demand for a certain good is high, it will be offered in close proximity to the population, and 3.)The world is an isotropic plain and that resources and people are distributed equally. Isotropic means that something has the same value when measured in different directions. However, these 3 assumptions are highly debatable. There are many contemporary examples where the certain cities or regions are not isotropic. On a global scale, resources are not distributed equally. MDCs have access to more resources and are able to obtain other resources and use those resources to manufacture goods. LDCs on the opposite end, do not have the same amount of access to resources as MDCs. Due to the lack of access to resources and lack of ability to develop resources into goods, LDCs do not develop as quickly. This is known as uneven development. Uneven development can also be observed on the city level. Within a city, usually the area directly surrounding the central business city is one of the poorest areas. These inner city areas often times remain poor and underdeveloped because they experience a process called ghettoization. Ghettoization is a process occurring in many inner cities in which they become dilapidated centers of poverty, as affluent whites move out to the suburbs and immigrants and people of color vie for scarce jobs and resources. This phenomena is also known as white flight. When the affluent whites leave the suburbs, they take all the wealth with them. This is what causes inner city decay. The tax base declines and inner cities become the center of poverty as a result of white flight and change in industry. A contemporary example of inner city decay would be in Chicago. Chicago has experienced sever inner city decay because as a city, Chicago is broke and its economy has crashed. Many people living in Chicago suffer from extreme poverty, and due to the extreme poverty, crime levels and violence are very high, making Chicago very hostile and unsafe. Families are attempting to escape the inner city in search of better conditions. This article in the New York Times takes a closer look at the deteriorating condition of Chicago, and how it's citizens have been affected.