Exploring the spatial connectivity of US states, 1993-2007

After a hiatus of almost 30 years, the publication of the interstate commodity flow data for 1993 afforded the first opportunity to examine the nature and strength of interstate connectivity in the US. While the New Economic Geography has provided new stimulus to understanding the spatial economy, complemented by new developments in trade theory that have highlighted geographical proximity, relatively little attention has been paid to the spatial structure of trade, especially at the inter-regional scale. Using data of 1993, 1997, 2002 and 2007, this paper explores various features of the spatial connectivity of the US states. The initial explorations focus on the concentration of the interstate trade system using simple Gini measures and then exploring the flow patterns with principal component analyses to examine the degree to which states share similar product origins or shipment destinations. Thereafter dyadic factor analysis is used to explore the flow structure for an aggregation of 13 commodities. One of the important findings from the analyses is that the general spatial pattern of interstate trade still reflects a geographical structure based on contiguity, with the notable exception of California.