Drawn in Red Ink: How Archival Maps and Municipal Records Are Quantifying the Geography of Segregation

A map is never a neutral document. When cartographers working for the federal Home Owners' Loan Corporation fanned out across American cities in the late 1930s to assess neighborhood lending risk, they produced something that looked like objective geographic analysis. Color-coded and annotated, the resulting maps assigned grades — green for desirable, yellow for declining, and red for hazardous — to residential districts across more than two hundred cities. The criteria used to determine those grades were not primarily geographic. They were racial. And the consequences of those designations, researchers are now demonstrating with unprecedented precision, can be traced in a continuous archival line from Depression-era filing cabinets to the present-day distribution of wealth across American metropolitan areas.

From Classification to Consequence

The HOLC maps themselves have been publicly known since the 1970s and digitized in high resolution through the Mapping Inequality project, a collaboration among several American universities that has made the documents freely accessible online. What has changed in recent years is not the availability of the maps but the sophistication with which historians are using them as entry points into layered archival research.

The maps, considered in isolation, document intent. The records that surround them — city council minutes, zoning ordinance amendments, property assessment ledgers, Federal Housing Administration underwriting files, and private bank loan registers — document execution. Researchers are increasingly treating the HOLC designations not as the story itself but as a coordinate system for navigating a much larger body of evidence about how segregation was administered, block by block, decade by decade.

At the core of this methodology is a relatively straightforward archival observation: the machinery of discrimination generated paperwork. Every zoning decision that restricted multi-family housing in white neighborhoods while permitting industrial encroachment into Black ones was recorded in a municipal ordinance. Every FHA loan guarantee denied to an applicant in a redlined district was documented in an underwriting file. Every property tax assessment that undervalued homes in disinvested neighborhoods — reducing the municipal services those neighborhoods received — was preserved in county assessor records. Taken together, these documents constitute something close to a complete administrative record of how segregation was built and maintained.

The Neighborhood as Unit of Analysis

One of the most significant methodological contributions of current digital history scholarship in this area is the use of the neighborhood, rather than the city or the metropolitan area, as the primary unit of analysis. Aggregate statistics about racial wealth gaps are well established. What archival research is now producing is something more granular and, in many ways, more damning: a property-by-property account of how specific policy decisions affected specific streets.

Research teams working in cities including Chicago, Baltimore, Detroit, and Richmond, Virginia, have constructed databases linking HOLC grade designations to property transaction records from county deed registries, decade-by-decade tax assessment histories, and municipal service delivery data drawn from public works department archives. The resulting datasets allow researchers to track, with considerable precision, the divergent trajectories of adjacent neighborhoods that received different HOLC grades in the late 1930s.

What those trajectories reveal is not subtle. In redlined districts, property tax assessments frequently declined relative to surrounding areas even as the physical condition of housing stock was comparable or improving — a pattern that reduced both homeowner equity and the tax base available for local school funding. Simultaneously, zoning records show that city planning departments consistently approved industrial and commercial uses in or adjacent to redlined Black neighborhoods at rates far exceeding approvals in green-graded white districts. The archive does not merely suggest that discrimination occurred. It records the administrative decisions through which discrimination was operationalized.

Real Estate Records and the Paper Trail of Exclusion

Private real estate records present particular opportunities and particular challenges for researchers working in this field. Restrictive covenant documents — deed provisions explicitly prohibiting the sale or rental of property to Black buyers — were recorded in county deed registries as standard legal instruments. Many remain in those registries today, legally unenforceable since the Supreme Court's 1948 ruling in Shelley v. Kraemer but not physically expunged from the record. Researchers have used geographic information systems to map the distribution of these covenants against HOLC grades, finding — predictably but importantly — that the two systems reinforced each other with near-total geographic overlap in many cities.

More recent archival work has turned to the records of private real estate boards and professional associations, some of which are held in university special collections. Internal correspondence and membership directories from organizations like local chapters of the National Association of Real Estate Boards document the professional enforcement of racial exclusion through steering practices, refusals to show properties, and the explicit professional sanctions applied to agents who sold to Black buyers in restricted areas. These records provide the human infrastructure behind the bureaucratic apparatus.

Connecting the Archive to the Present

The evidentiary value of this research extends into contemporary policy and legal debates. Several municipalities have commissioned or supported archival studies of their own redlining histories as part of reparations research initiatives or fair housing litigation. In these contexts, the granular nature of the archival record matters enormously. Demonstrating that a specific neighborhood received a specific HOLC grade, that grade was followed by specific zoning decisions, those decisions were accompanied by specific patterns of loan denial, and those patterns produced measurable declines in property value and tax revenue — this chain of documented causation is qualitatively different from arguing that discrimination occurred in the abstract.

Digital history tools have been essential to making this kind of analysis tractable. The volume of records involved — tens of thousands of property transactions, hundreds of zoning decisions, years of tax assessment histories — would be impossible to analyze manually at neighborhood scale. Machine learning approaches to document classification, combined with GIS mapping, have allowed research teams to process archival materials at a scale and speed that opens genuinely new historical questions.

The Archive as Accountability

What the redlining archive ultimately offers is not a new argument but an old argument made newly precise. Scholars have argued for decades that American residential segregation was not an organic social phenomenon but an engineered policy outcome. What archival research is now providing is the documentation to support that argument at the level of individual streets, individual properties, and individual administrative decisions.

The records were created by the institutions that designed and enforced segregation. They were preserved, often inadvertently, in county courthouses, municipal archives, and federal record centers. Reading them carefully — and reading them together, across record types and jurisdictions — is the work that Project Past exists to support: the recovery of a history that was always documented, even when it was never intended to be known.