(b) if the proposed additional or relocated motor vehicle dealer is to be within a county having a population of less than one hundred thousand, the area within the radius of ten miles of the intended site of the proposed or relocated dealer. Such ten mile distance shall be determined by measuring the distance between the nearest surveyed boundary line of the existing new motor vehicle dealer's principal place of business and the nearest surveyed boundary line of the proposed or relocated new motor vehicle dealer's principal place of business. In determining the population of a county, the most recent census by the U.S. Bureau of Census or the most recent population update, either from the National Planning Data Corporation or other similar recognized source, shall be used.