Concentric zone model was the first urban model to explain the process of the placement of zones and social classes in cities, and also explained how cities grew. The model was created by Ernest Burgess in 1925. The model picutres cities as divided into circular zones all centered around the Central Buisness District(CBD). The first circle was the CBD, the other circles were either factory zones, residential zones, or transition zones. This urban model was eventually succeded by the Sector Model.