Edward Ullman

Edward Louis Ullman (1912 – 1976) was an American geographer. He proposed that trade was an interaction based on three phenomena: complementarity, intervening opportunities, and transferrability of commodities.

The level of interaction can be measured by the Gravity model of trade:

$I_{i,j} = \frac{p_ip_j}{d_{i,j}^\beta}$

Where:

I: Level of interaction between i,j. alternatively, quantity of trade between i,j.
P_i = population of i
D_i,j = distance separating i,j
β = impedance factor

External links

University of Washington

Persondata
Name	Ullman, Edward
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Date of birth	1912
Place of birth
Date of death	1976
Place of death