Ullman, Edward Louis,  1912-1976 <br/><br/>
American commodity flow :  a geographical interpretation of rail and water traffic based on principles of spatial interchange / 
by Edward L. Ullman 
 - Seattle :  University of Washington Press,  1957 
 - xxii, 214 p. :  ill., maps ;  23 cm. 
<br/><br/>Includes bibliographical references (p. 207-213) and index 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Transportation--United States
<br/><br/><label>Subjects--Geographic Terms: </label><br/>United States--Commerce