The Spatial Economy: Cities, Regions, and International TradeThe authors show how a common approach that emphasizes the three way interaction among increasing returns, transportation costs, and the movement of productive factors can be applied to a wide range of issues in urban, regional, and international economics. Since 1990 there has been a renaissance of theoretical and empirical work on the spatial aspects of the economythat is, where economic activity occurs and why. Using new toolsin particular,