[Excerpt] Industry clusters are associated with greater job hopping and faster growth in workers’ earning power relative to the experience of workers at less spatially concentrated companies. Workers in these clusters tend to accept lower starting salaries than peers at more isolated firms in anticipation of rapid gains that accompany movement from job to job within the cluster and the accumulation of industry-specific knowledge. Higher earnings observed among workers in clustered firms may also reflect choices made by workers with certain characteristics to seek employment in an area with a high concentration of similar firms and by companies with certain characteristics to locate in such an area.