For statistical purposes, the consolidated city-county is organized into 99 "neighborhood areas" with most containing numerous individual historic and cultural districts, subdivisions, and some semi-autonomous towns. In total, some 500 self-identified neighborhood associations are registered in the city's Registered Community Organization system.[126] As a result of the city's expansive land area, Indianapolis has a unique urban-to-rural transect, ranging from dense urban neighborhoods to suburban tract housing subdivisions, to rural villages.[127]
Typical of American cities in the Midwest, Indianapolis urbanized in the late-19th and early-20th centuries, resulting in the development of relatively dense, well-defined neighborhoods clustered around streetcar corridors, especially in Center Township.[128] Notable streetcar suburbs include Broad Ripple, Irvington, and University Heights.[129] Starting in the mid-20th century, the post–World War II economic expansion and subsequent suburbanization greatly influenced the city's development patterns. From 1950 to 1970, nearly 100,000 housing units were built in Marion County, most outside Center Township in suburban neighborhoods such as Castleton, Eagledale, and Nora.[129]