Maps.com (Firm) & ebrary, Inc. (1999). U.S. population change, 1950-1970. Maps.com.
芝加哥风格引文Maps.com (Firm) 与 Inc ebrary. U.S. Population Change, 1950-1970. [S.l.]: Maps.com, 1999.
MLA引文Maps.com (Firm) 与 Inc ebrary. U.S. Population Change, 1950-1970. Maps.com, 1999.
警告：这些引文格式不一定是100％准确.