“Urbanized area” means a central city or a group of contiguous cities with a population of 50,000 or more, together with adjacent densely populated areas having a population density of at least 1,000 persons per square mile. A lead agency shall determine whether a particular area meets the criteria in this section either by examining the area or by referring to a map prepared by the U.S. Bureau of the Census which designates the area as urbanized. Maps of the designated urbanized areas can be found in the California EIR Monitor of February 7, 1979. The maps are also for sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. The maps are sold in sets only as Stock Number 0301-3466. Use of the term “urbanized area” in Section 15182 is limited to areas mapped and designated as urbanized by the U.S. Bureau of the Census.