Theory is divided on whether falling transport costs lead to more or less spatial concentration of economic activity. Using US county-level data we find that aggregate employment became more concentrated between 1972-92. This aggregate picture hides important differences between sectors though....

Using US county data, we estimate employment growth equations to analyze how the spatial distribution of jobs has changed between 1972 and 2000. We find that total employment has become increasingly concentrated. This aggregate picture hides important sectoral differences though: whereas...