For statistical purposes, this area is specifically defined for individual cities. Because there are not generally accepted rules for determining what a CBD area should include or exclude, the U. S. Bureau of the Census did not provide rigid specifications for defining the CBD but provided a general characterization of the CBD, describing it as an area of very high land valuation; an area characterized by a high concentration of retail businesses, offices, theaters, hotels, service businesses; and an area of high traffic flow; and required that the CBD ordinarily should be defined to follow existing census tract lines; i.e., to consist of one or more whole census tracts.