There wasn't ever a single person or agency that centrally dictated redlining, nor were the actual maps with their stark color coding widely distributed to lenders at the local level. In a way the Federal Housing Administration (FHA), the most influential federal agency involved in redlining, "enforced" certain rules by only insuring loans on homes that met its racist appraisal standards. But local lenders already engaged in similar practices, so it was more of a bilateral reinforcement of existing discrimination.
While those "red lined" maps offer a useful and compelling illustration, the concept of redlining usually refers more broadly to the entire institution of mortgage discrimination against neighborhoods based on their racial makeup. The most infamous maps were those drawn up by the Home Owners' Loan Corporation, a federal agency created as part of the New Deal in 1933 to help reduce foreclosures. The maps rated the creditworthiness of various neighborhoods by color coding and grading them from A-D.
The FHA was founded a year later and mostly took over the duties of the HOLC. The FHA's job was to guarantee nearly all the collateral on qualifying mortgages, vastly reducing the risk to the lender and reducing costs to buyers. Together with a corresponding Veterans Affairs initiative and the HOLC, these programs established the precedent for long-term (e.g. 30-year) mortgages with only a small amount due as a down payment. With the subsequent creation of Fannie Mae, those loans could be easily sold on a national exchange to buyers across the country.
In order to get an FHA secured loan, a home had to meet certain standards that, in aggregate, favored white suburban homes. The FHA gave favorable terms to loans for new homes over those for renovations and it approved loans more often for for single-family units than, for example, rowhouses commonly found in cities. Most importantly, the property had to be appraised with an "unbiased professional estimate" before the FHA would insure the mortgage. For this purpose it provided its Underwriting Manual with precise appraisal guidelines, listing "inharmonious racial or nationality groups" as a factor that could adversely affect the "economic stability" of a neighborhood, and stating "if a neighborhood is to retain stability, it is necessary that properties shall continue to be occupied by the same social and racial classes." The manual also encouraged racial covenants, written agreements between home buyers and sellers guaranteeing the home would never be sold or rented to minority groups. In this way, lenders didn't have to actually see any maps, they only needed to know if a home or neighborhood was likely to get FHA approval.
The FHA certainly received copies of the HOLC maps and used them as a source when creating maps of their own. But there is little reason to believe any FHA or HOLC maps were widely distributed. Historian Kenneth Jackson did the seminal work on the HOLC maps in the 1970s, but prior to that they were not widely known or discussed. The vast number of mortgage lenders operating nationwide, the size and complexity of the physical maps, and records that show the HOLC was careful about who received copies, all indicate that individual mortgage lenders were unlikely to have their own copies. But as mentioned, lenders didn't need access to the actual maps for the FHA's policies to have the net effect of reinforcing existing neighborhood boundaries and encouraging white suburban flight.
The numbers speak for themselves. Early FHA data is only available on a county-by-county basis, but the trends are still clear. In New York City through 1960, for example, FHA-secured loans amounted to $10 per capita in the Bronx and $53 in Brooklyn, compared with $601 per capita in suburban Nassau County. Through 1966 there was not a single FHA secured loan in Camden or Paterson, New Jersey, both former industrial cities that experienced significant white flight through that period. Similar results can be seen city after city across the nation. For the first 30 years of its existence, the FHA backed more than 15% of all mortgages in the US, with peaks in years of economic recession.
That said, while the federal government unquestionably played a central role in the redlining of neighborhoods, it would be wrong to think of it as the originator or propagator of these ideas. Maps with borders drawn around neighborhoods and language about the risks of mixed-race neighborhoods can be found in guides for realtors decades before the FHA, and racial covenants have been attached to deeds in the US dating back to the 19th century. Political scientist Michael Jones Correa cautions against reading redlining as a one-way exchange of ideas:
As HOLC and then the FHA got underway, they were staffed at the federal and local levels by former real estate professionals who operated under and accepted the profession's racial strictures, and who then transferred these norms into federal practices. For example, Frederick Babcock, a prominent figure in real estate appraisal, who wrote a widely used appraising text The Valuation of Real Estate (1932) advocating the enforcement of racially segregated neighborhoods, went on to write the FHA's 1938 Underwriting Manual, which incorporated similar assumptions of the desirability of neighborhood homogeneity and the pernicious influence of black home ownership on property values.
From the outset redlining was always a two-way exchange between localized actors and federal institutions. Rather than being a top-down enforcer of redlining, the federal government was more of an equal partner in crime. It took existing discriminatory practices, both written and unwritten, and made them explicit and normalized them for use by lenders across the country.
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This isn't a question I feel quite capable of doing justice to, since it is something I've read a bit about, but not to the point of feeling capable of diving into the complexities beyond the parroting of others. I do however, have a reading recommendation if you want to dive into the topic yourself. The color of law: A forgotten history of how our government segregated America, by Richard Rothstein, I found to be an absolutely excellent read looking at both de facto, and, more importantly, de jure mechanisms through which segregation and discrimination through real estate was maintained through the 20th century. I'm quite in agreement with Johanna Hanley's review, when she concludes "Despite the complexity and level of detail covered throughout this book, it is accessible for a variety of audiences", and that really does speak volumes as it is a balance point that few books are able to hit just right, and it is hard to go more than a few pages without being floored by what you're finding out as you progress through it.
Probably its biggest strength is the focus on what you are asking about, since while the de facto factors are ones which are fairly well understood, the de jure gets much less notice in popular understanding, and Rothstein's focus is on bringing that aspect of the history into the forefront, and which he manages to do quite ably, "artfully captur[ing] the historic context and highlights the structural racism pathways that further elaborate contemporary conditions on health and housing nexus". That popular narrative is one which reinforces an idea of "suburban innocence", and as almost every review harps on, allows for something of an evasion in popular memory of just who was culpable for what happened, and the sheer breadth at which it occurred, and Rothstein essentially turns it on its head, "arguing that the real history of segregation is primarily that of explicit or de jure government policy, with personal actions secondary".
As with any book, it isn't without its criticisms, but they are quite mild. The main point of contention is less any imputation of error than it is Rothstein's insertion into a still running academic debate over the impact of the Fair Housing Act's passage in 1968 and how effective it has been since then in reversing the impact of discrimination previously. Rothstein, perhaps unsurprisingly, sees it as mostly ineffective in achieving those goals, as do many other scholars, but some other recent works have a softer view, seeing the FHA as having helped reduce real estate segregation after is passage, but even this it must be noted we're talking in degrees, as none argue it came close to actually eliminating it. But even Gale, who gave probably the most pushback of the reviews I consulted, is still willing to call it a "magisterial work" that "stands as a powerful indictment of governmental duplicity in obstructing free choice in the sale and rental of housing for all Americans" and joke they feel they are committing apostasy by criticizing such a well done book!
So while this isn't quite the direct answer to your question, hopefully it does encourage you to seek out Rothstein and give him a very worthwhile read, as it is essentially a book-length treatment of what you are asking about.
Reviews consulted*
Avila, E. and Irfan, A. (2021), Rothstein, Richard, The Color of Law: A Forgotten History of How Our Government Segregated American. New York: Liveright, 2017. pp. 368. ISBN-13: 978-1631492853S.. World Medical & Health Policy.
Callison, J. W. 2017. The color of law: A forgotten history of how our government segregated america. Journal of Affordable Housing & Community Development Law 26, (1): 5-11,
Gale DE. Review: The Color of Law: A Forgotten History of How Our Government Segregated America by Richard Rothstein. Journal of Planning Education and Research. 2019;39(3):380-381.
Johanna Hanley (2019) The color of law: A forgotten history of how our government segregated America, Journal of Urban Affairs, 41:8,
Pekoll, James. 2017. The color of law. A forgotten history of how our government segregated america. The Booklist 113, (15) (Apr 01): 4,