Since 2014, the City Sector Model has been used to portray population trends by functional area within the 53 major metropolitan areas (major metropolitan areas). The current edition classifies small areas (zip code tabulation areas) by demographic factors into five categories (Figure 1). The first two are urban core (central business district and inner ring), while the last three are suburban or exurban. The suburban areas are largely within the continuous built-up urban areas, while the exurban areas are generally in the metropolitan areas, but outside the built-up urban areas.
Image: http://www.newgeography.com
