Based on surveys asking people whether they thought the lived in urban, suburban, or rural ares, Trulia economist Jed Kolko has defined the borderline between urban and suburban as 2,213 households per square mile (slightly less than 3.5 per acre), while the line between suburban and rural is 102 households per square mile (about 1 household every 6.3 acres). Based on this, Kolko concluded that less than half of many cities are truly urban.
Specifically, as shown in an article in Slate, 100 percent of New York, Chicago, San Francisco, Detroit, Washington, Boston, and Baltimore are urban. But less than half of Phoenix, San Antonio, Indianapolis, Columbus, Fort Worth, Charlotte, El Paso, Louisville, and Tucson are more than 70 percent suburban. Only 3 percent of Seattle, but 43 percent of Portland, are suburban.
Kolko isn’t the first to define urban and suburban using demographic rather than political criteria. The Antiplanner’s faithful ally, Wendell Cox, did a similar analysis last year. Looking at urban areas rather than cities, he defined areas as pre-auto, early auto, late auto, and exurban. The pre-auto areas included all areas with a median home construction date before 1945, areas with more than 7,500 people per square mile, and areas where non-auto commute shares exceeded 20 percent. The early auto areas were those remaining areas with median home construction dates before 1979; late auto had median home construction dates after 1980; and exurban was all land in the metropolitan statistical area but outside the urbanized area.