Edward Ullman

From wiki.gis.com
Jump to: navigation, search
Multiple nuclei model by Chauncy Harris and Edward Ullman

Edward 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}


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

External links