This map comes from Field Notes III of the Detroit Geographic Expedition & Institute (DGEI) which had a series of maps and features on the Cass Corridor. The last Cass Corridor map noted the racial differences in Cass Corridor. This map illustrates the racial divide where Black population rarely crossed 3rd Avenue to reside within the Cass Corridor.
The Cass Corridor was considered a “society” neighborhood in the 1860s – 1900s as Lewis Cass sold his farm land and the wealthy began building large Victorian homes there. In the 1960s – 1970s it was considered one of the pockets of White population in the city.
From DGEI’s Field Notes III publication:
“But, physical proximity has done little to bring the white Appalachians of the corridor any closer to blacks socially. Their dislike for each other has a long history, which stretches back to the days when they were both poor in the South. Poor whites and blacks have always had to compete with each other for jobs. An “outsider” may be able to see their mutual hatred as a trick played to keep them from uniting. To them, it is a deeply rooted cultural feeling.”
DETROITography 
Interesting. What data is the map based on, and what’s the source of the quotation? Re: white Appalachians, I highly recommend John Hartigan’s anthropological study of white Detroiters in the early 1990s, “Racial Situations: Class Predicaments of Whiteness in Detroit.” Hartigan found that the white “hillbillies” of the Briggs neighborhood (now “North Corktown”) were in many respects more open to cross-racial interaction than their Corktown neighbors.
This map was published in “Field Notes III” by the Detroit Geographic Expedition & Institute (DGEI), who also collected the data in 1971.
The Cass Corridor was a “Planned Slum.” The Old Michigan Avenue Skid Row was demolished in the 1950s as part of Urban Renewal. There was a small Chinatown there that was caught up in the Mix and knocked down (although it was reportedly thriving.) So-THEN, many white alcoholics moved to the Cass Corridor, while some of the poor African Americans moved to the Twelfth Street Area, which also took in Refugees from the Demolition of the Black Bottom and Hastings Neighborhoods. When I attended Wayne State, the panhandlers would beg on Campus. There were also prostitutes of both races in the Lower Corridor. Mario’s Restaurant weathered the Storm, despite being adjacent to old apartment buidlings. Cass Corridor’s Skid Row was concentrated around Third and Myrtle. MANY buildings burned or were demolished. The local Fire Station was nicknamed “Devil’s Island.” The Low-Rise Condo Style PJs of the Jeffries Projects were along Fourth Street. Heroin-and then Crack Cocaine-were a problem in this neighborhood.
Note that the 1971 quotation and maps here are from my article, “The Children of the Cass Corridor,” in the DGEI Field Notes III. I did the fieldwork myself door to door in the Cass Corridor and constructed the ownership map from public records.