There are many limitations and statistical uncertainties in making a full interpretation of the Omaha Trade Area, but we plan to go as far as we can to bring together the commonly used indicators that show the sphere of influence of a major trade center. A number of indicators, such as retail sales, newspaper circulation, correspondent banks, grain shipments, etc., will be mapped individually. Then, for the final analysis, a composite map will be constructed to show the area of overall dominance by Omaha.
Retallick, Harold J. and Gildersleeve, Charles R., "Omaha Trade Area Study No. 02: An Analysis of Telephone Calls, Newspaper Circulation, and Correspondent Banks" (1967). Publications. 13.