Columbia subject headings:
Census districts--United States--States.
U.S. states--Statistics--Methodology.
United States--Census, 1990.
Harvard subject headings:
Census districts--United States--States.
U.S. states--Statistics--Methodology.
United States--Census, 1990.
Princeton subject headings:
Census districts--United States.
Regional planning districts--United States.
United States--Census, 1990.