Vacant and abandoned properties clustered on the Chicago’s South and West sides and southern suburbs have been a stubborn problem for decades. Every two years, the Cook County treasurer tries to return those properties to productive use during its biennial scavenger sale of delinquent taxes, often with little luck.

A new analysis from a team at Treasurer Maria Pappas’ office sought to find out why. Their answer: Federal “redlining” maps that sanctioned discriminatory lending policies in the late 1940s correlated strongly with sites of vacant and abandoned properties today.