Did the HOLC draw maps with red lines on them around neighborhoods where they thought mortgage loans were going to go bad? Yes.
Were those maps used to deny loans in the areas with red lines around them? Certainly not by the HOLC, and almost certainly not by the FHA or private lenders.
Was there racial discrimination by the HOLC? Maybe. Less than with other mortgage lenders of the day.
Was there racial discrimination by the FHA? Yes. Mostly block by block based on census data and New Deal projects that collected data. They did make their own maps, but that's hard to research since those maps were mostly destroyed in the 1960's. The ones that survive don't match the HOLC maps. There's some overlap.
Were there racial covenants? Until 1948, yes, that's not redlining though.
Do the maps made by the HOLC in the 1930's explain violent crime in Chicago in the 2020's? No. Not at all.
