Sally is very interested in her city. She likes to walk around a lot and has noticed that there are distinct neighborhoods that seem to serve different purposes. There are areas with a lot of skyscrapers and businesses, and areas with factories and low-rise buildings. There are areas where people live in apartment buildings, and areas where people live in houses. Every area of her city seems different to Sally!
An urban area is a place with a high population density and mostly non-agricultural jobs. That is, there are a lot of people and not very many of them work in farming and ranching. Like most other cities, Sally's city is an urban area.
How are urban areas arranged? Sally has noticed different neighborhoods, but she wonders how the neighborhoods are laid out on a map. To understand the way that urban areas, like Sally's city, are arranged, let's look at three popular models of urban structures: the concentric zone model, the sector model, and the multiple nuclei model.