Over the past century, many models have been made to explain urban social structures of a city. Created in 1923 by sociologist Ernest Burgess, the Burgess concentric ring model, also known as the Concentric zone model or the CCD mode, is one of the earliest theoretical model made and used to explain the structure of a city. This model is a very simple one based on the city of San Francisco in the 1920s. Below is an image of the CCD model on Google Sketchup with the link attached to it.
In the model above, we see five different colored rings; pink, turquoise, green, grey, and burgundy. The pink center is the central business district (CBD), it is where all the business and trade happens. The CBD is also where the malls and expensive shopping and dining halls, which are mostly accessed by the elite residents, are located. The next ring, the turquoise ring outside the CBD, are the factories and industries. This is where all the goods are manufactured and sent off to the CBD to be sold for a profit.
Outside the factories we have the low income residents. In the picture above, we can see that the houses in the low income residential area are all cramped together. This is because there were many many people belonging the the low income residential area, causing a lack of space. The only solution to this problem was to build tinier houses and make the area more cramp. The low income residential area also live closest to the central business center and the factories because they are not rich enough to afford cars, thus most of them either walk to get to places or they take streetcars. Then we have the middle income residents living outside the low income residential area. The middle income residential area have houses that are more spread out and spacious.
Lastly, we have the elite residents/ high income residential section. As you can see in the image at the very top, the elite residents have extremely spread out houses with many trees, parks, and other entertainments such as swimming pools in between. The elite residents live furthest away from the CBD because they were able to afford cars to travel to places. At the time this model was created, cars were a new thing, so they were extremely expensive. Only the richest of the rich could afford them, which were most of the people living in this area.
There is a link at the very top that will lead you to the Google Sketch-up Pro file of the Burgess Concentric Ring model.