Reform and Consequence: The Mid-Century Roots of Twenty-First-Century Zoning

Introduction

In the twenty-first century, most cities use a Euclidean zoning model that regulates use (sorted by single-family residential, multi-family residential, commercial, and industrial)—and dimensional standards (lot size, setbacks, building height, etc). These zoning codes include multiple districts to regulate development intensity and maintain orderly, compatible growth. However, as Euclidean zoning remains the dominant approach, criticism grows.

Many scholars critique U.S. zoning for producing land-use-segregated suburbs that fuel sprawl, reduce walkability, ¹ limit housing diversity, and constrain affordability, often attributing these problems to zoning’s origins a century ago. ² This paper brings forth evidence that the decisive shift toward auto-oriented, exclusionary suburban models emerged not from zoning’s initial adoption but from mid-twentieth-century shifts supported by technological changes, expanded utilities, growing automobile prioritization, and the vast financial and legal powers introduced through Urban Renewal. While early zoning ideologies were influenced by exclusionary attitudes and aspirations for suburban-style development—reinforced by movements like Better Homes and decisions such as Euclid v. Ambler—early ordinances lacked both the funding and legal tools needed to reshape existing cities at scale. As a result, established cities initially implemented zoning by balancing planning goals with preexisting, walkable urban fabrics. Mid-century reforms enabled the large-scale restructuring of cities in ways early zoning advocates could not achieve, making them the true turning point in the evolution of contemporary zoning systems.

It is important to note that the research question of this study fundamentally changed during data collection. The first goal of the study design was to investigate evidence supporting claims made by previous authors regarding zoning’s discriminatory origins being evident in the first zoning ordinances. ³ However, as the research continued, little explicit evidence of exclusionary code language was found in zoning ordinance archives across cities from 1900 to 1930. Instead, these early documents reflected the kind of code advocated for by many planners in the twenty-first century—pedestrian-scale mixed use with housing opportunity. This posed an important research question to determine when this fundamental shift occurred and under what influence?

This study presents findings derived from both deep archival research and spatial analysis tracking zoning map and demographic trajectories that key elements of twenty-first century zoning—such as the predominance of single-family zoning, large lot sizes, deep setbacks, distinct use separation, and auto-oriented design—largely came about during mid-century updates funded by Urban Renewal policies supporting parallel comprehensive planning procedures. Mid-century reforms laid the groundwork for many zoning issues that twenty-first century planners, such as the New Urbanist, smart growth, and walkable cities movements, seek remediation for: exclusionary practices, reduced housing choice, poor pedestrian access, mandated sprawl, and reduced long-term sustainability. ⁴ By comparing original zoning ordinances to their mid-century revisions and twenty-first century codes, we can better understand how zoning evolved and why many concerns persist.

This paper postulates three reasons for this shift. First, early zoning emerged in a pre-automobile context, when most city dwellers relied on walking, public transport, or animal-drawn options. Second, early planning ideologies often conflicted with existing urban fabric and couldn’t be fully implemented without provoking rights’ challenges. Third, early zoning lacked the funding and authority needed to enforce widespread change. At the time, communities were largely self-contained: residents lived, worked, and attended school within walkable neighborhoods. The later Urban Renewal-era court precedents and legislative authorities that empowered cities to enact forceful policies for implementation were forthcoming.

In the 2020s, proposed reforms seeking solutions to sprawl, housing choice, and pedestrian access often face counterarguments that existing zoning is too entrenched to change. However, history shows that zoning ordinances have changed before—and dramatically so. If cities once shifted away from walkable, mixed-use design in favor of suburban single-use and auto-oriented patterns, they can reverse course again. Looking to early zoning models may offer valuable insights for crafting a more accessible and sustainable future.

Discussions on Zoning’s Evolution and Twenty-first Century Critiques

Many have assessed the structure and efficacy of Euclidean zoning, with frequent attribution to zoning’s initial roots. Euclidean zoning is characterized by the separation of land uses into distinct categories such as single-family residential, multi-family residential, commercial, and industrial. ⁵ Twenty-first century models also impose detailed regulations on physical site design, including requirements for lot size, building setbacks, height limitations, and other dimensional standards reflective of NYC’s 1916 first comprehensive ordinance. Typical standards for these codes now reinforce auto-oriented design through street orientations, high parking requirements, disconnected land uses and properties, and large lot sizes. These complex and detailed ordinances, characterized by rigid divisions of land use, reinforced by development standards, produces a typical suburban-style land use design. ⁶

Euclidean zoning codes have been the brunt of widespread criticism in recent years. The production of land-use-divided suburbs perpetuating sprawl and lack of walkability are a key consideration. ⁷ Authors denounce zoning’s perpetuation of large single-family lots and the impacts on both growth management and the environment. ⁸ Others criticize the lack of opportunities for use-mixing and creating landscapes that do not support transit-oriented development. ⁹ Zoning also arose as a key component in discussions on housing affordability and access, ¹⁰ contributing to the ongoing crisis by limiting missing middle housing, restricting housing diversity/densities, and reinforcing residential disenfranchisement. ¹¹

Early zoning intended to promote orderly development and ensure compatible land uses, aiming to create predictable, stable urban environments with ample green space and low-density development patterns. ¹² Thus, some argue that the environmental concerns of zoning originated with the first zoning laws. ¹³ There is no denying that the aspirations of early zoning ideologies to generate suburban-style development were in place at the early twentieth century. The Better Homes movement of the early 1900s was quickly taken up by policymakers at all levels of government, pushing for reductions in density and more open space. ¹⁴ Yet, the resulting codes combated longstanding urban landscapes and the realities of lifestyles for early twentieth-century households when seeking to divide land uses and standardize development. Therefore, the codes perpetuating sprawling suburbia arose later in the twentieth century.

In thematic discussions on the costs and consequences of zoning, it is often implied or directly stated that twenty-first century exclusionary zoning issues also originate a century ago. ¹⁵ Early adoption at the end of the City Beautiful and Progressive movements reflected a time known for deep racial and class segregation, further highlighting the likelihood of zoning ordinances reflecting these patterns. ¹⁶ Conversations surrounding early zoning objectives were shaped by exclusionary ideologies targeting people of color and lower-income populations, reflected in federal publications and the Euclid v Ambler Supreme Court decision. ¹⁷ However, these ideologies were not supported with funding and the legal foundations for eminent domain to enact desired urban form was yet to come. ¹⁸

This study began with the question: What code language was included in these early codes to begin the trajectory of these trends? However, the search for evidence of this causation in historic zoning ordinances reveals that early codes more closely resemble the walkable mixed-use twenty-first century planners are advocating for. Talen identified this discrepancy, but attributed it to zoning’s first authors valuing a broad spectrum of uses and housing choice. ¹⁹ However, while this could have been the case for some early zoning advocates (such as Ed Bassett), this paper suggests that the trajectory of zoning stemmed not from shifting ideologies so much as shifting technologies (i.e., improvements in utilities and prioritization of the automobile) alongside resources to reshape existing urban fabrics through Urban Renewal policy sponsorship unavailable in the first decades of the twentieth century that enabled a mid-century shift toward suburbanization models with distinct use separation and auto-oriented design.

Post-WWII attorney, and later legal scholar, Seymour Toll reflected in his 1969 book that the mid-century turn was an ideological revisitation of the original excitement for the residential ideal that drove early zoning adoption. ²⁰ In the 1960s looking backward, he believed that the early health and wellbeing motivations for zoning were quickly reverted into real estate tools engaged in socio-economic preservation by removing industry from residential spaces—what was then termed “snob zoning” as an early form of NIMBY-ism. However, he does precursor the conclusions of Rothstein’s ²¹ later seminal work when he suggests that to discuss industry is to discuss ethnicity given the workforce demographics of the early twentieth century city. Babcock’s 1966 Zoning Game further revealed the perceptions of bias and leniencies ingrained in zoning processes by that point that led to some calls for reform. ²² That he revisited this concept for a twenty year-post sequel suggests that the mid-century reforms were unsuccessful in resolving these issues. The findings here support the idea that planners of the 1960s were eager to return to an updated concept of the ideal suburb, and are able to expand further on Toll by reflecting on the enabling factors and impacts of those mid-century changes.

Established cities contended with implementation of first zoning ordinances by balancing between planning objectives versus the existing pedestrian-oriented lifestyles and urban fabrics of now-regulated spaces. Thus, many features of twenty-first century zoning did not appear until mid-century shifts supported by technological advances, court allowances surrounding Urban Renewal, and large financial packages as part of the implementation of new comprehensive plans funded with Urban Renewal grants, rather than in zoning’s first iterations.

Methods

This paper uses a comparative case analysis of two cities reflective of how zoning evolved in major U.S. cities, then reviews additional cities with similar characteristics to identify shared patterns. The broader evidence suggests that the study’s conclusions reflect nationwide zoning trends in large U.S. cities that initially adopted Euclidean zoning in the early twentieth century.

Identifying two representative cities required a rigorous review to ensure they met characteristics necessary for a temporal zoning analysis. Additional criteria ensured the cases could illuminate how zoning intersected with race and class dynamics—a central concern in zoning reform. The selected cities met the following criteria:

Few U.S. cities meet criteria 1–8, and only two also satisfy criteria 9–11 regarding comparable population, city age, and regional representation. San Antonio and Philadelphia meet all requirements: both were founded in the colonial era, were roughly 200 years old when adopting zoning, have similar populations of about 1.6 million (the 6th- and 7th-largest cities nationally), and represent the Southwest and Northeast regions.

The research drew on several years’ review of over 300 primary sources from public and private historic archives, accessed through municipal Open Records Requests and through collections at the University of Pennsylvania, the University of Texas (Austin and San Antonio), City and County clerks’ offices, the Smithsonian, and the Library of Congress. Key materials included multiple iterations of historic zoning maps, generations of zoning codes, and all amendments over time. Additional primary documents—City Council and committee minutes, city reports from internal and external organizations, historic and Sanborn maps, photographs, and adopted city plans—were also examined. The examination of archival materials considers changes in zoning practice and the impacts of these changes on permitted land development and accessibility.

While the research focused on primary source regulatory, policy, and planning documents, complementary materials such as firsthand narratives, media publications, political statements, letters submitted to the City Councils, site reviews of construction during the twentieth century, and other archival collections further informed the analysis. Historic secondary sources and academic literature deepened contextual understanding.

The investigation initially focused on identifying language in early zoning ordinances that perpetuated sprawling land use patterns and exclusionary practices during initial zoning adoption. As the review progressed, notable shifts in zoning language and structure from the first iterations to mid-century reforms surfaced, prompting deeper inquiry into their origins and effects.

Initial investigations made clear that Urban Renewal played a central role in reshaping zoning law in both cities, prompting major code overhauls in the 1960s that produced many of the patterns now widely criticized. This led to further examination of (1) how each city restructured its zoning code, (2) how zoning ordinances and district distributions changed following Urban Renewal, and (3) the durability of these changes, assessed by comparing mid-century reforms with current zoning. Additional archival research on the three eras distinguished: (4) the cities’ motivations for adopting their original codes, including (4a) how those codes were designed to accommodate existing development and expected growth; (5) each city’s approach to Urban Renewal and (5a) how these policies shaped the adoption of a second, mid-century code generation; (6) the goals guiding the development of the third, twenty-first century code iteration, along with broader city conditions throughout the twentieth century.

Finally, supporting GIS data closest to the date of each zoning code overhaul and investigating demographic shifts at the ten-year census intervals provided an opportunity to investigate changes in social and economic conditions. Multifarious spatial analysis focused on temporal shifting of how the cities distributed different residential districts, placement of high-intensity land uses, and the relationship of zoning to demographic distributions. Areas that experienced Urban Renewal projects were of particular interest. The analysis of each city identifies neighborhoods of change and stability that are further explored.

While the study focused closely on two primary comparison cities, the same methods were applied to other cities meeting criteria 2–8 to assess whether similar patterns emerged. Findings from the two cases, reinforced by this broader review, highlight national trends, clarify motivations behind dramatic zoning changes in the mid-century, and solidify Urban Renewal’s influential role in shaping twenty-first century zoning systems.

Tracing Zoning’s Trajectory

Deep archival and spatial research reveal a distinct trajectory of zoning law in U.S. cities that first adopted zoning prior to WWII. The purpose of this research was to investigate for evidence of the claims made by authors regarding the language of early zoning that would perpetuate across the twentieth century as the foundation for contemporary zoning concerns. Instead, the findings reveal a fundamental shift in permitted land uses and development standards, driven by shifting conditions following World War II and supported by mid-century policy actions. This fundamental shift away from pedestrian-scale mixed-use regulations toward auto-oriented suburban landscapes resulted in many of the challenges faced by twenty-first century planners.

Two case cities model this national trend in zoning timelines: (1) first adoption during the 1930s of a pedestrian-scale, largely mixed-use ordinance retrofitted onto existing landscapes, (2) adoption of Urban Renewal policy funding new comprehensive planning documents (3) a 1960s revised code regulating for auto-oriented and suburban land use patterns, and (4) an update in the early twenty-first century that reflected an incremental shift back toward the first iteration codes.

Both cities drafted their original ordinances under Harland Bartholomew’s influence after state adoption of the Standard State Zoning Enabling Act. These codes separated some land uses but still supported walkable, mixed-use development despite the Euclid v. Ambler (1926) decision’s endorsement of Euclidean zoning. Records from the period show city leaders and planners grappling with existing urban form, human and animal-based transportation modes, and property rights conflicts from new regulations on land development. Then, despite local differences, both cities exhibited a clear intent during 1950s policy and ordinance amendments to eliminate previous patterns of walkable, mixed-use development with diverse housing types. During the 1960s, new ordinances ultimately replaced the first iterations with conventional Euclidean zoning divisions that separated commercial, single-family, and multi-family uses in auto-oriented urban design during the mid-century shift. Resulting zoning ordinances encouraged office-park complexes, commercial box and shopping strips patterns, and disconnected single-family subdivisions. Twenty-first century comprehensive plan and zoning code updates seek resolution to consequences of these auto-focused ordinances, but only slightly modify use and development standards away from 1960s reforms. Similar movements arose in cities with shared characteristics.

Philadelphia

The Philadelphia Zoning Code evolved across three ordinances adopted in 1933, 1962, and 2012 with many minor changes between these dates. Despite three code iterations, zoning history in Philadelphia can be divided into two distinct eras: 1933 to 1962 and 1962 to contemporary zoning. The divide between the early zoning era and the modern one was a reform prompted by the city’s Urban Renewal policies.

Initial Adoption

The first era featured a lenient approach to non-conforming mixed-use and multi-family properties that existed prior to the adoption of zoning. ²³ The original zoning ordinance, adopted August of 1933, contained seven residential zoning districts, four commercial districts, and two industrial districts (see Figure 1). By 1955, the original seven residential districts expanded to twelve districts further delineating the classifications of housing. The ordinance appeared to divide the city along conventional Euclidean lines but typically permitted uses in districts outside of their primary purpose (i.e., office in residential, etc.). The zoning ordinance and map encouraged multi-plex housing and live-work structures.

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Figure 1.

The original zoning districts from the Philadelphia Zoning Map of 1933.

The 1933 Philadelphia Zoning Map shows extensive coverage of A–D districts, often spanning entire neighborhoods, while E districts (typically squared-off apartment buildings) were scattered throughout. Each of Philadelphia’s first seven zoning districts allowed a mix of housing types and accessory commercial uses. Mixed-use development was not only allowed but expected, as evidenced by frequent code provisions detailing the design of mixed-use buildings. All A–E districts required large setbacks (at least 20 feet) and limited lot coverage (under 50 percent). Though notably C–E multi-family zones were concentrated near industrial parks, rail lines, and other areas designated for heavier or hazardous uses, it was still relatively abundant. The limited use of “F” zoning suggests planners saw this inclusive development as unsuitable for broad application.

The city’s diverse housing stock, present before zoning, persisted through nonconforming uses and frequent Board of Adjustment variances during early planning years, 38,500 variances and special exceptions from 1933 to 1957. ²⁴ Land development slowed to a halt in Philadelphia in the early 1930s as the nation managed the Great Depression, reinforcing the importance of existing housing stock. ²⁵ City leaders focused efforts on rehabilitation and reducing vacancies as funding dragged for other options. Still, the city faced a growing need for more housing, particularly in its urban core, as rural Americans moved into cities.

During the later 1930s, housing reform advocates discussed the need for modernized housing solutions in Philadelphia. Black community leaders from the NAACP and NNC, alongside New Deal Public Works Administration programs, backed housing condition improvement programs. ²⁶ This empowered city leaders to identify areas needing reform, with small federal grants awarded from 1934 to 1937.

Mid-century Reform

Following World War II, construction and housing reform redoubled. As suburbs flourished, older cities like Philadelphia targeted slum clearance. To oversee this new approach, the city changed its charter, transformed the Planning Commission, and drafted a 1942 comprehensive plan flooded with redevelopment goals. The city accepted large Urban Renewal grants following the passage of the 1949 Housing Act to fund these efforts. ²⁷

To support new residential development patterns, Philadelphia introduced three H zoning districts in 1953. ²⁸ These districts established a new category known as “Group Dwellings,” permitting a mix of housing types and accessory uses within a single development. Added at the beginning of the Urban Renewal era, the H districts facilitated “tower in the park” projects with some mixed-use. Alongside the introduction of a “cottage” housing option (C-1) in 1954, these changes allowed developers to diversify the city’s housing stock. High-density multifamily zoning proved especially valuable as the city redeveloped underutilized parcels, including the construction of numerous public housing projects. ²⁹

However, resistance from affluent residents led to quick shifts toward suburban-style developments. In 1954, the city created the AA district designed for extra-large single-family homes. The H districts’ flexibility was short-lived; in 1955 the city removed permission for community-serving uses such as schools and professional offices, effectively ending their mixed-use potential.

The changing H codes foreshadowed shifting planning ideologies. 1956 saw several urban-renewal focused studies of land use throughout Philadelphia (and other cities nationwide). One of these, the Philadelphia’s Central Urban Renewal Area (CURA) Study, was directly tied to use of Urban Renewal funds. An additional study, part of a nationwide assessment, shined light on the shifting landscape of the Center City area. ³⁰ A third study during this year assessed the placement and impacts of industrial and quasi-industrial uses and the need to attract higher-earning households and high-paying employers as most new development occurred in Montgomery County rather than on underused parcels within Philadelphia. ³¹

In 1957, the Bureau of Municipal Research studied Philadelphia’s zoning, directing the focus of reform toward regulations. ³² Their report summarized an assessment of both code language and administration. It concluded that the city’s zoning was “in need of a thorough overhauling.” A key critique was insufficient legal basis for zoning without a comprehensive plan or any guidance for hearing bodies about how to make their decisions. The report included a jab at the members of the city’s Zoning Board of Adjustment and Planning Commission, stating that “businessmen and housewives” are not equipped to know the best planning decisions. The Bureau’s critique accelerated drafting of a new ordinance that again preceded a comprehensive plan.

City auditors scorned the Board of Adjustment’s approval of use variances rather than bringing properties into compliance. The Bureau for Municipal Research dedicated thirty-seven pages in its fifty-six-page report to lament variance approvals with a clemency toward multi-family housing and non-conforming uses. The report claimed that the high number of variances granted by the Zoning Board of Adjustment for these uses was perpetuating blight and downgrading neighborhoods. The authors felt that the continued unanimous approval of use variance requests was so troublesome that it strongly urged staff to draft recommendations influencing the Board of Adjustment to deny any further cases.

Other policy suggestions included increasing zoning fees and targeting funds to eliminate existing non-conforming multi-family and mixed-use properties altogether through demolition. They recommended taking steps toward bringing more properties into compliance through the “removal of nuisances” through eminent domain. Philadelphia would take this up the following decade leading to widespread devastation of mixed-use and multi-family communities. ³³

Substantial Urban Renewal funding and planning guidance supported a 1962 zoning overhaul to reform procedures and slow growing blight and stem business flight to the suburbs—a trend confirmed in the 1956 land-use studies. ³⁴ Adopting zoning amendments prior to completion of the city’s outdated comprehensive plan or even sub-area plans undermined planning best practice and the guidance issued in the Standard State Zoning Enabling Act. Yet, Philadelphia was not alone in its eagerness to utilize Urban Renewal funds, reorient their codes for auto-based development, and remove low-income slum development regardless of the age and quality of their comprehensive plans. Additional use of Urban Renewal funding supported aggressive government removal of non-conforming uses in the 1960s thus ensuring twenty-first century urban design reflects the revised ordinances of the twentieth century. ³⁵

The second era of zoning intensified the separation of land uses in line with Euclidean theory. The new zoning map clustered multi-family housing with commercial uses rather than single-family zones, and single-family districts lost nearly all accessory-use allowances. The ordinance explicitly aimed to create suburbanized development by separating living areas from work and commercial spaces.

Middle housing options—such as rowhomes, manufactured housing, townhomes, and cottage clusters—received dismissive treatment. A special district for “trailer camps” stated its purpose was to “maintain stringent control on the establishment of trailer camps within the City.” ³⁶ Notes created to help residents interpret the ordinance showed a clear bias for separating single- and multi-family housing, reflected in split districts (e.g., R-9/R-9A and R-10/R-10A) where low-density multi-family uses were allowed in one but not the other, often in response to complaints from single-family rowhome owners. ³⁷ Although the 1962 ordinance expanded the number of districts to cover various housing types, middle and apartment housing still faced more restrictions than single-family homes. Requirements included large minimum unit sizes—especially for duplexes and other middle housing—mandatory yard space for each unit even in multi-family buildings, and added parking barriers such as bans on adjacent parking and mandates for specific paving materials. ³⁸

From 1963 to 1973, Philadelphia produced sub-area plans justifying both regulatory and procedural changes. In 1965, the city drafted a comprehensive plan funded by Urban Renewal grants, but zoning enforcement under the 1962 code was already in full motion. As a result, the plan largely reflected actions already underway rather than charting a future vision—a pattern seen in other city documents from this period. As the city transformed, new legal precedents upholding its planning practices increasingly overrode resistance from long-standing businesses and residents. ³⁹

By November 1, 1973, the zoning code had changed substantially from its 1933 version. The original residential categories were renamed as “R” districts: R-1 matched the old AA district that allowed only detached single-family homes, R-2 replaced the former B district, and so on. ⁴⁰ The city also added a new district to allow 24-foot-wide rowhouses—the single-family housing type long favored by many middle-class residents. In 1973, the city created five new districts allowing commercial and office uses on the ground floor of apartment buildings. This echoed patterns from the first zoning ordinance, except these districts were now removed from neighborhood interiors and clustered around Center City.

Although the zoning code described apartment and mixed-use districts as essential to city planning goals, after 1962 they could only be established through ad hoc Council rezoning and were never proactively mapped by planners. Multi-family developments were treated as a commercial enterprise rather than housing, an approach rooted in Euclid v. Ambler but not in Philadelphia’s early zoning. At times, the city even used demolition for enforcement. From 1962 to 2012, the zoning code required ad hoc approval for only three other uses besides multi-family or mixed-use housing: airports, quarries, and landfills—each considered high-intensity. ⁴¹ It was not until a 1982 amendment that dumping landfill waste was banned on residential lots. In practice, multi-family housing faced stricter control than landfills. ⁴²

In the 1980s, the city adopted three “Conversion Districts” to allow subdivision of large single-family homes into multi-family units. However, like other multi-family districts, these could only be applied through an ad-hoc rezoning process, placing the burden on property owners. Rezoning approval also required large unit sizes and community support. A later amendment eliminated previously available density bonuses in the R-16 and RC districts, further limiting opportunities for higher-density housing.

By 1998, the code included thirty-eight base districts, including ten single-family categories. The city created alternate residential districts (R10A, R10B, and R9A) in the 1970s and 1980s to curb rowhome conversions to reduce use of the R10 and R9 middle-housing districts. R-14 no longer allowed apartments despite multifamily designation of R11 through R16.

In 2012, Philadelphia undertook major zoning reforms with a new zoning ordinance. With a stronger focus on planning equity, the city aimed to create a more user-friendly code and streamline the many districts and amendments added since the 1962 overhaul. This purpose for a third reform iteration is reflected across other sister cities like Detroit. The new ordinance included innovative mixed-use districts of varying intensity (RMX and CMX) districts, but planners reserved application of these districts for limited areas near Center City.

Mapping of Philadelphia’s zoning districts before and after the 2012 ordinance highlights both the imbalance in land area designated for single-family versus multi-family housing and that the distributions of zoning districts remained relatively unchanged following the code conversion in 2012 (Figure 2). ⁴³ This varies greatly from the assessment of paper maps from 1933 compared to the maps adopted in 1962 which shifted land dedication to more single-family zoning. Following October 1, 1962, large portions of the city previously zoned “C” and “D” (middle housing with accessory light commercial uses) have been reserved exclusively for single-family use. While Philadelphia remains unique in its significant allocation of land for middle housing types, particularly row homes, 78 percent of single-family detached zoning is located in areas buffered from hazardous uses. By comparison, only 46 percent of middle housing and 21.88 percent of apartment zoning enjoy similar protection. ⁴⁴

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Figure 2.

Before and after the 2012 Philadelphia zoning ordinance adoption.

After first adoption in 1933, Philadelphia’s zoning code underwent numerous changes, with three major iterations and numerous ad hoc amendments. However, its history reflects two distinct eras: 1933 to 1962 and 1962 to the present. The first era favored mixed land uses and leniency toward non-conforming multi-family housing that predated the code. The second era, shaped by Urban Renewal and following advances in technology, imposed stricter Euclidean zoning, systematically removed non-conforming uses, and leveraged public funding to reshape the city’s built environment.

San Antonio

Like Philadelphia, San Antonio underwent three major zoning iterations beginning in the 1930s. Between 1938 and 1965, the city used a simple code that separated housing from commercial and industrial uses, while still allowing limited mixing of low-intensity uses within residential zones. In the 1960s, the city’s Urban Renewal Commission led a zoning ordinance overhaul, funded by federal Urban Renewal funds. The 1965 ordinance reinforced strict use separation, prioritized automobile access, and promoted suburban-style development. It also guided the growth of thousands of newly annexed acres over the following decades. In 2001, San Antonio adopted a Unified Development Code, which eliminated most mixed-use potential outside the Downtown area, further encouraging suburban expansion. ⁴⁵ Although recent amendments allow limited mixed-use development on a case-by-case basis, most new construction still follows traditional Euclidean zoning.

Before zoning, land use in San Antonio was characterized by walkable, mixed-use development. The 1896 Sanborn Maps show industrial, commercial, and residential uses located side by side. At the time, the city was relatively small, limiting potential to separate uses or distinguish neighborhoods by socioeconomic status. From 1890 to 1930, San Antonio’s population grew from 37,673 residents to 231,541, prompting an expansion of the city boundaries and new construction. A major contributing factor to this boom was the relocation of families to San Antonio to be near military bases during World War I. ⁴⁶

Initial Adoption

Looking to confront rapid growth, San Antonio’s City Council approved the Public Welfare Department’s request to pay Harland Bartholomew $18,000 from the General Fund to begin crafting zoning for the city on July 7, 1930. ⁴⁷ Bartholomew was joined by men from the San Antonio wealthy elite, including Freemason master & businessman G. G. Grabenheimer and philanthropist Nat Goldsmith. ⁴⁸ These men had conflicting ideologies. Grabenheimer and Bartholomew encouraged a rational-comprehensive approach, but Zoning Commission Chairperson Goldsmith pushed for public involvement. Reaching compromise, the city passed its first zoning ordinance on November 3, 1938.

The first zoning code established thirteen zoning districts (Figure 3): one single-family district (A), two middle housing districts (B & C), two apartment districts (D & E), six commercial districts (F-K), and two manufacturing districts (L & M). All residential districts required ample setbacks of at least 25 feet. ⁴⁹ Commercial/industrial uses adjacent to single-family lots were held to a higher setback requirement than apartment uses. Common during this period, the city utilized a hierarchical structure of zoning that cumulated uses in successive districts (Figure 3). ⁵⁰

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Figure 3.

The hierarchical structure of the 1933 San Antonio zoning ordinance.

The San Antonio ordinance embodied characteristics reflective of the period. Like the Philadelphia ordinance, the type of accessory uses allowed reveals the class of people living on these parcels. Non-conforming uses in all districts could continue in perpetuity. These details show a code modeling the socio-economic structures and existing urban fabric countering regulatory efforts.

San Antonio was racially segregated between 1930 and 1965 as the first zoning ordinance was implemented. ⁵¹ Black communities were (and still are in 2025) isolated east of downtown, Mexican communities (40 percent of the population) were in the west and south parts of the city. The housing stock in these areas was old, in bad repair, and overcrowded (though single-family). ⁵²

Mid-century Reform

The 1938 Zoning Code remained largely unchanged through World War II, guiding development during a period when the city grew but lacked the resources or political momentum for major land-use reform. That shifted in 1957, when San Antonio voters approved participation in the federal Urban Renewal program. The city’s chamber of commerce and real estate board strongly promoted the initiative, emphasizing the availability of federal funds for slum clearance and redevelopment. Their support, combined with low voter turnout and limited public engagement, produced an overwhelming victory for Urban Renewal at the polls. ⁵³

Participation in the federal program ushered in a transformative period for the city. Urban Renewal funding and authority enabled San Antonio to clear large swaths of older neighborhoods, reshape street networks, and reposition land for new development. This momentum catalyzed a second era of zoning in San Antonio aligned with mid-century planning trends marked by comprehensive revisions to the city’s land-use framework and a shift toward auto-oriented, suburban-style development patterns that would define the decades that followed.

San Antonio stood alone among major Texas cities in accepting federal Urban Renewal funding. ⁵⁴ This distinction may stem from the city’s much older urban core—roughly 125 years older than Dallas, Austin, Fort Worth, and Houston—which faced significant deterioration by the 1950s.

As economic decline intensified, especially downtown, city leaders pushed for aggressive slum clearance and large-scale reconstruction in the central city, West End, and near-east neighborhoods within the original 8 square miles. Instead of involving the City Planning Commission, San Antonio empowered a newly formed Committee on Slum Clearance and Urban Redevelopment to draft both the city’s comprehensive plan and its second-generation zoning ordinance. ⁵⁵ This committee also oversaw clearance and redevelopment activities. Census records from 1960 show that targeted neighborhoods were among the lowest-income areas and home to large Mexican and Black communities. ⁵⁶ The outcomes varied widely: much of the cleared land remained underused for years due to limited funding or weak business interest. One area containing 274 Mexican families was cleared for future central business uses, according to City Council records, but ultimately became the site of a county jail, courthouse, and police department. Another major clearance zone was redeveloped for the 1968 World’s Fair (see Figure 4).

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Figure 4.

A neighborhood of Mexican Americans designated for demolition, future site of HemisFair Park, San Antonio.

On June 28, 1965, San Antonio adopted a new zoning code as part of its Urban Renewal–driven comprehensive plan, drafted not by the City Planning Commission but by the Committee on Slum Clearance and Urban Redevelopment. ⁵⁷ The ordinance arrived at a pivotal moment: San Antonio had recently become the first southern city to desegregate its lunch counters and, in the same year, passed an ordinance integrating all public facilities. ⁵⁸ Yet, while the city advanced social justice in some policy areas, its new zoning code reinforced a vision of traditional, single-family, middle-class suburban development.

The 1965 zoning ordinance created 12 new zoning districts: three single-family districts (R-A, R-1, and R-5), a duplex and a mobile home district (R-2 and R-4 respectively), one apartment district (R-3), four commercial districts (B1 to B-4), and two industrial districts (I-1 and I-2). The shift to increase the number of single-family districts and decrease the number of multi-family districts spoke to the city’s shifting priorities to establish and maintain more single-family suburban-style areas. This was foreshadowed by the city’s removal of middle-housing zoning districts from the original ordinance between 1954 and 1964.

Text from the second iteration zoning ordinance suggested that the city considered middle and apartment housing types unsuitable for neighborhoods. The 1965 zoning code defined only one-family and two-family zoning districts as creating a “suitable neighborhood development for family life.” ⁵⁹ For mobile home districts, the zoning code stated that the district was intended to protect the surrounding development from the mobile home sites (Section 42-71). This mentality creates a legal structure where those living in these residences are a use that must be protected against, rather than households in need of protection. Apartments and other similar multi-family or non-traditional single-family homes were likewise restricted.

As the development regulations shifted in 1965, the codified definitions of family also changed. In the original 1938 zoning code, the definition of family could include extended family, servants, or unrelated individuals. The 1965 zoning code changed this to restrict relationships by adding language requiring the household to be “in a domestic relationship based upon birth, marriage, or other domestic bond.” ⁶⁰ This restriction sought to distinguish residential units from boarding houses and hotels. However, this type of code language is known to disproportionately impact Queer, Black, Indigenous, Latinx, women-led, and low-income families. ⁶¹

The language of the 1965 ordinance reveals a city trying to balance two goals—promoting suburban growth and reassuring existing property owners. The regulations ensured that newly annexed areas would develop along suburban lines, while providing sixteen pages of extensive allowances for nonconforming uses and vested rights that protected older neighborhoods from immediate change. While the city developed 643 acres from 1930 to 1960 under the first ordinance, the suburban-style would soon become the dominant development pattern of the city as 8,242 acres (12.88 square miles) of land developed under the new 1965 ordinance into auto-oriented, single-use spatial patterns. ⁶² This growth challenged city utility capacities, such as fresh water supply and electricity demand, creating problems that twenty-first century planners would spend billions to address.

In 1980, San Antonio deliberated the draft of a new Master Plan at length. Conflicting ideologies in the city delayed the process, a very different undertaking than the single-minded Urban Renewal mid-century plan. The resulting policy document was weak and made little headway to direct the rapid development of the city. Instead, political influence and lobbying controlled development approvals in the latter half of the twentieth century. ⁶³

Neither the 1980 Master Plan nor the 1997 update anticipated how extensively San Antonio would sprawl, especially across the city’s northern half. Although the city adopted new regulations for suburban-style development, planners expected these standards to guide infill within existing city limits and recently annexed areas inside Loop 410—not to trigger large-scale annexation of county land far beyond Loop 1604. As a result, development in the expanded city boundaries grew to include wide suburban subdivisions and major commercial centers, including the luxury shopping complex known as The Rim. Had a land use plan guided growth during these decades—particularly in the city’s ETJ—much of this sprawl likely would not have occurred. ⁶⁴

Rapid growth and changing city leadership prompted San Antonio to create a Unified Development Code in 2001. This third generation code remains in place, allowing a diversity of development types—if they conform to traditional auto-oriented Euclidean ideologies. Amendments since 2001, including removal of impervious cover limitations and adding infill type zoning districts, are incorporating more options into the code to try and bring about the walkable, sustainable development patterns wished for in the 2016 SA Tomorrow comprehensive plan. ⁶⁵

San Antonio’s zoning history is long and layered, producing a complex twenty-first-century Euclidean code. The city’s approach began in 1930, driven by Harland Bartholomew’s vision of Euclidean zoning tempered by limited legal authority, resources, technologies, and community voices. Then, a second-generation ordinance informed by Urban Renewal policies guided post-war development enabled by advances in transportation, construction, utilities, and legal authority, which encouraged sprawling, suburban-style development throughout the latter half of the twentieth century. Across both eras of zoning, low-income communities and people of color experienced disproportionate impacts as a legal tool that reinforced San Antonio’s long-term de facto racial and income segregation—creating what Richard Rothstein would likely describe as a de jure disparate impact. ⁶⁶

A Common Zoning Story

Despite regional differences, Philadelphia and San Antonio share a set of core characteristics also found in other major U.S. cities. Both anchor large metropolitan regions, are minority-majority cities with deep colonial histories, and have long depended on significant industrial sectors. When examined together, they reveal regulatory patterns common among cities with similar profiles. Both cities adopted zoning in the 1930s—after the Standard State Zoning Enabling Act and the Euclid v. Ambler (1926) decision—and both relied on planning work produced under Harland Bartholomew. Each city then moved through three major zoning eras.

Beginning in the 1930s, zoning maps in both Philadelphia and San Antonio showed a consistent patterns for regulating housing. Their first-generation zoning codes, adopted in this period, followed a hierarchical model in which single-family residential zones—often designated “A”—were defined as the least intense and therefore most protected while placing higher levels of density and more affordable housing types near industrial uses. This hierarchy privileged single-family areas while allowing working-class housing in industrial or heavy commercial districts, a practice common across many U.S. cities. Census data from 1940, 1960, 1980, and 2000 confirms that these distributions aligned with socio-economic patterns throughout the twentieth century. Despite these protected enclaves, the larger portions of land in these cities permitted mixed-use by-right with pedestrian-focused development patterns to allow for both live-work properties and accessible service industries in neighborhoods.

The second zoning codes adopted in the 1960s in both cities were funded and driven by Urban Renewal and drafted largely by Urban Renewal committees or staff, redirecting development toward auto-oriented, suburban-style patterns. These mid-century codes intensified the separation of land uses and housing types, diverging sharply from the more flexible 1930s ordinances; although they technically preserved districts allowing a broader mix of housing, such districts were rarely applied. National guidance from organizations like the American Society of Planning Officials encouraged cities to prioritize new construction over rehabilitation, reinforcing planners’ postwar push to separate multi-family, commercial, and single-family uses—a departure from the walkable, mixed-use fabric that had characterized most U.S. cities. The third-generation codes adopted in the early twenty-first century made only minor adjustments to uses and development standards and remain in place in 2025. Together, the cases of Philadelphia and San Antonio show how Urban Renewal fundamentally reshaped zoning in ways that discouraged walkability and mixed-use development, with lasting effects still visible into the twenty-first century.

In these details, Philadelphia and San Antonio reflect broader national patterns. Other major U.S. cities followed similar trajectories: New York City (1961), Detroit (1964), Salt Lake City (1960), and Winston-Salem (1968), among many others, also rewrote their zoning ordinances post-World War II. Like the case cities, these jurisdictions used federal Urban Renewal grants to finance the work and relied on Urban Renewal agencies to guide the regulatory overhaul. Their goals aligned: replace walkable, mixed-use development with clearly separated, auto-oriented land-use patterns concurrent with expanding highway infrastructure and protect single-family residential neighborhoods while clearing so-called “slums.”

Urban Renewal marked a major turning point in zoning and urban development. Beginning with the Housing Act of 1949 and lasting through 1974, federal policy provided cities with loans and grants to radically reshape their physical landscapes; more than $13 billion in redevelopment spending flowed to cities during this period. Many municipalities used these funds as an opportunity to revise their zoning codes, adopting regulations that aligned with emerging ideas of “modern” urban form.

Several social and economic forces shaped these mid-century zoning reforms. The rapid rise of automobile ownership encouraged cities to replace walkable, mixed-use neighborhoods with auto-dependent suburban development, a shift made possible by postwar population growth, the availability of undeveloped land, with advances in utilities and construction. Generous federal funding enabled the large-scale demolition and reconstruction of entire neighborhoods, while simultaneous highway construction reinforced these changes by targeting older, non-conforming areas—disproportionately low-income communities of color—for clearance. These developments unfolded alongside the Civil Rights Movement and desegregation efforts, which further influenced redevelopment priorities and, in many cases, intensified exclusionary impulses. City reports and meeting minutes from the era openly reflect racist and classist motivations: officials sought to control the spread of “undesirable” people living in so-called slums, labeled low-income housing a nuisance even when single-family, and deemed neighborhoods outside the white middle-class norm as blighted. It is no coincidence that many areas targeted by Urban Renewal were the same neighborhoods redlined three decades earlier, underscoring how racialized and class-based structures deeply shaped this zoning revolution.

The regulatory context preceding Urban Renewal also played a significant role. During the initial adoption of zoning in the early twentieth century, cities relied heavily on race-based deed restrictions, redlining, and segregation laws—particularly after the U.S. Supreme Court ruled race-based zoning ordinances unconstitutional in the 1917 Buchanan v Worley decision. Because other tools enforced racial and class separation, land-use zoning itself did not initially need to play this role. Only later—after segregation laws and deed restrictions were ruled unconstitutional—did many communities turn to zoning as a mechanism for exclusion, relying on single-family districts and other restrictive practices to achieve similar effects. As cities accepted Urban Renewal funding and cleared neighborhoods labeled as “slums,” they reshaped both their zoning codes and their physical landscapes in ways that excluded many of the residents who had lived in the areas targeted for clearance.

The evolution of multi-family zoning across these periods reflects shifting attitudes toward housing and desired development. When zoning was first introduced in the 1930s, middle housing and apartment buildings were common throughout both cities, often integrated within residential blocks and interspersed with commercial uses as demonstrated by the widespread non-conformance of multi-family structures post-zoning adoption. Evidence from Philadelphia reinforces this: during a four-week observation of the Board of Adjustment in the 1940s, multi-family housing comprised 43 percent of all cases, yet no residents voiced opposition. This suggests that planners—not the public—drove early resistance to multi-family development. In many neighborhoods, long-standing development patterns included a mix of housing types and uses; zoning regulations, rather than property owners, created the conditions that labeled these structures non-conforming.

Both case cities, alongside many of their sister-cities, have since created mixed-use zoning districts primarily available through ad hoc zoning procedures similar to those seen in other cities. Though these codes seemed innovative, the development patterns they permit are consistent with what existed in the cities prior to the adoption of zoning in the 1930s. In many cases, these developments are limited to certain geographic areas and face significantly restricting development standards.

Unique Patterns of Growth

The differences in the two cities create two distinct regulatory typologies shared by sister cities. In particular, the land development patterns of Philadelphia and San Antonio diverged significantly throughout the twentieth century, representing regional differences. When zoning was first adopted, San Antonio was considerably smaller than Philadelphia—covering just 36 square miles compared to Philadelphia’s 135. Over the second half of the twentieth century, San Antonio undertook extensive annexation while Philadelphia’s boundaries remained largely fixed. As a result, San Antonio now spans 505 square miles, whereas Philadelphia covers just 141.7. These divergent trajectories reflect broader regional patterns: San Antonio’s growth mirrors that of many southwestern and midwestern cities that expanded outward through annexation during periods of rapid population increase, while Philadelphia’s stability in land area—and eventual population decline—resembles the experience of rustbelt cities with long-established borders.

These differing spatial and historical dynamics had important implications for the zoning evolution of each city type. Many differences in the evolution of zoning codes stem from their respective development and settlement patterns at the time of initial zoning adoption. Philadelphia-type cities (Detroit, New York City, Baltimore, etc.) added zoning to a built-out city, creating many non-conforming properties. These dense 1930s cities had aging housing stock and limited capacity to accommodate automobile-oriented infrastructure. Faced with this existing urban fabric, city leadership celebrated empowering funding and jurisdictional authorities granted during Urban Renewal to demolish and retrofit auto-based zoning. In contrast, San Antonio-type cities (San Deigo, Dallas, Charlotte, etc.) developed much more acreage after zoning’s adoption. Post-annexation, auto-oriented growth occurred beyond the original square miles. Non-conformance concerns in those older areas arose only after the second and third generation of zoning codes.

An additional factor contributing to the divergence in zoning outcomes among cities is the difference in state legislation and court rulings following mid-century changes. For example, in 1977, the Pennsylvania Supreme Court decision in Surrick v. Zoning Hearing Board of Upper Providence established a “fair share” requirement for multi-family housing, similar to the Mount Laurel decisions in New Jersey. By 1988, Pennsylvania and other states’ law required municipalities to zone for multi-family housing proportionate to their total land area. This contrasted with Texas and other home-rule states. This legislative difference contributed to some regions having proportionally more land zoned for multi-family and mixed-use development than others. The effect is especially noticeable in San Antonio’s newly annexed areas, which are almost exclusively zoned for single-family housing with limited supporting retail. These legal differences shaped zoning reform and resulting development across cities during the twentieth and twenty-first centuries.

Conclusion

The two cities, San Antonio and Philadelphia, provide insight into how mid-century shifts in policy and funding fundamentally reformed U.S. zoning ordinances. Following this pattern, cities can investigate their own zoning ordinances and histories for evidence into how mid-century policy shifted urban design away from the early urban fabric footprints. Many of the neighborhoods that are most loved in our cities were constructed prior to the suburbia-emulating zoning codes that emerged during the later twentieth century. ⁶⁷ As twenty-first century cities look to reclaim the walkable, mixed-use footprints that existed prior to zoning, undoing the components of mid-century reform, in ways that avoid the repeats of the past articulated by mid-century contemporaries, can return regulatory patterns back toward pedestrian-oriented cities.

The history of zoning in the United States reveals that many of today’s challenges—such as exclusionary practices, limited housing diversity, and sprawling, auto-oriented development—are not solely rooted in the original intent of early zoning codes but are largely the result of mid-twentieth-century reforms driven by Urban Renewal during a period of rapid technological transitions and when the original excitement around zoning had turned stale. ⁶⁸ Represented here by Philadelphia and San Antonio, early zoning ordinances permitted more flexibility, mixed-use development, and a wider range of housing types. However, postwar political ideologies, federal redevelopment policies, and planning approaches enabled significant restructuring of zoning systems, enforcing rigid land use separation and prioritizing suburban-style growth. These changes not only reshaped the physical form of cities but also entrenched patterns of social and economic segregation. Understanding this historical trajectory is essential for today’s planners and policymakers. It challenges the perception that current zoning systems are immovable and offers evidence that zoning has changed before—and can change again. Revisiting the more adaptable and progressive principles of early zoning could provide a valuable foundation for crafting more equitable, sustainable, and livable cities moving forward.