In the shadow of a Shinto torii gate in São Paulo's "Japanese" neighborhood sits the city's oldest "African" slave cemetery. Scholars have shown that urban spaces like these both reflect and help to construct cultural identities, but we know less about the range of social and spatial actors who do the constructing. My research examines how official urban planners (employed by state or development institutions) and unofficial urban planners (local residents) gave meaning to racial/ethnic identities by creating, inhabiting, and modifying spaces in mid-twentieth-century São Paulo. Official planners' urban renewal projects in the late 1930s widened avenues, demolished homes, and raised property values in center-city neighborhoods like Bixiga and Liberdade. Displaced residents migrated to cheap lands on the urban periphery and built new neighborhoods like Brasilândia independent of official planners. These related official and unofficial planning activities occurred in neighborhoods that became racialized/ethnicized in the decades following as "Japanese" Liberdade, "Italian" Bixiga, and "African" Brasilândia. Employing historical geographic information systems (HGIS), oral history, and archival analysis, my research endeavors to uncover the array of official and unofficial planning practices that contributed to the making and cultural marking of these neighborhoods. São Paulo's diverse population and polarized development patterns make it an auspicious site for tracing broad participation in the co-production of cities and cultural identities. By bringing a novel conception of planning as a set of practices to an apt historical case, my work challenges the formal/informal dichotomy in urban studies and elucidates the underappreciated relationship between urban planning and culture over time.