The maps in this post are part of a grim history. They were created by a government program in the 1930s and played a role in keeping African Americans and other minorities from owning property in American cities, thereby leaving an indelible mark on the racial and economic history of the United States.

Now, for the first time, hundreds of these maps and documents are available online in one place.

The collection, called Mapping Inequality, includes maps and notes from the Home Owners’ Loan Corporation, a federal program established during the Great Depression to shore up the housing market.

The HOLC was tasked with figuring out the investment risks in various cities so banks could determine where to give out loans.