The 1937 Home Owners’ Loan Corporation map of Baltimore — the original “redlining” document in which the government determined which neighborhoods were worthy of mortgage lending — is reproduced, in full color, on Page 73 of the scathing federal investigation of the city’s modern-day police force released this week.

It seems, perhaps, an odd inclusion, a housing history lesson in a report on policing, an 80-year-old artifact far removed from the city’s dynamics in 2016. But this map is, if not the beginning, part of an early chapter in explaining how things in Baltimore got where they are, full of racial mistrust and deep chasms between poor, black neighborhoods and city institutions. It is directly connected to the city’s policing problems today.

The Baltimore Police Department’s recent “zero tolerance” policing strategy focused, the Justice Department report points out, on neighborhoods that have been segregated for decades and that were created in the first place by government policy:

City leadership encouraged and supported this segregation by passing the country’s first block-by-block segregation ordinance, which made it a crime for African Americans to move to majority white blocks, and vice versa. At the time of the ordinance’s enactment in 1910, the New York Times described it as “the most pronounced ‘Jim Crow’ measure on record” and noted that “[n]othing like it can be found in any statute book or ordinance record of this country.” The Supreme Court later struck down a similar ordinance in Buchanan v. Warley, 245 U.S. 60 (1917), but the effect in Baltimore was minimal. White property owners, with support from City leadership, continued to enforce the rule informally by requiring homeowners in certain white neighborhoods, like the affluent Roland Park area in North Baltimore, to sign covenants barring African Africans from owning or renting their property. The mayor directed City building and housing inspectors to institute a practice of citing for code violations anyone who rented or sold property to African Americans in those neighborhoods.

Federal mortgage policies both restricted blacks to segregated neighborhoods and prevented them from building wealth there. They later explicitly excluded blacks from homeownership in the newly built suburbs. They fostered the twin troubles of segregation and poverty.

Because these patterns remain in Baltimore today, they have essentially created a city map conducive to discriminatory policing. Compare the above map to this one, also from the report, showing reported Baltimore police stops in the city in 2010-2015, with neighborhoods colored by their percentage black population (red neighborhoods are more than 65 percent black):

The citys entrenched segregation also created a set of social forces that police have been ill-equipped to handle.

“When cops hear that they have the burden to address racism and poverty and education and homelessness,” former Baltimore police commissioner Anthony W. Batts is quoted as saying in the report, “I think cops misinterpret that message with, ‘how do you expect me to do that?’ ”

That may be expecting too much of police (especially when we don’t invest in their training around those issues). But while navigating such historic forces is difficult, it is very easy in a highly segregated city to know exactly where the lines are drawn between communities receiving “zero tolerance” and those meriting gentler treatment.