Policy researchers often have to estimate the future effect of imposing a policy in a particular location. There is often evidence on the effects of similar policies in other jurisdictions but no information on the effects of the policy in the jurisdiction in question. And the policy may have specific features not reflected in the experiences of other areas. It is then necessary to combine the evidence from other locations with detailed information and data specific to the jurisdiction in question, with which to simulate the effects of the policy in the new jurisdiction. We illustrate and use this approach in estimating the impact of a proposed living wage mandate for New York City, emphasizing how our ex ante simulations make use of detailed location-specific information on workers, families, and employers using administrative data and other new public data sources.