Answers are grounded in this paper and cite their sources.
(1971). THE NATIONAL ATLAS OF THE UNITED STATES OF AMERICA. Annals of the Association of American Geographers: Vol. 61, No. 4, pp. 791-793.
No takes yet. Share an insight, caveat, or question.
George F. Jenks (1971) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: