Understanding who is investing in real estate, and the patterns of their investments, is critical both for assessing the need for, and the effects of, policy interventions by governments, lenders, and non-profit community development organizations. If we knew more about patterns of ownership, for example, we could target buildings that seem to "produce" disproportionate numbers of homeless families seeking housing in the City's shelter system. Many other policies could also be made more effective, including policies related the city's property tax assessment, water and sewer lien practices, outreach to small property owners for energy upgrades, enforcement of rent regulation rules and policies to encourage investment through tax subsidies and zoning changes. Not only is understanding these patterns critical for deciding how to target interventions, but they may have significant implications for the effectiveness of interventions ranging from policing to the opening or closing of schools to land use policies such as inclusionary zoning. Copyright is held by the owner/author(s).