Special issue article Urban Analytics and City Science Neighborhood formation in St. Louis, 1930 John R Logan, Chris Graziul and Nathan Frey Brown University, USA Abstract What are the social bases of neighborhood formation in urban areas, and at what spatial scale are they most distinct from other neighborhoods? We address these questions in the case of St. Louis, Missouri, in 1930, where we can take advantage of unique geocoded census micro- data on the whole population of the city that identifies who, with what background character- istics, lived where. Our analyses show that homophily by race and ethnicity was by far the strongest factor linking characteristics of persons to the composition of their neighbors. Measures of social class also were quite important, while the person’s nativity and family status were statistically significant but minor predictors. Yet while this hierarchy of social factors held for the population as a whole, their relative importance varied greatly across racial/ethnic groups. Similarity in social class to neighbors was most important for native whites, nativity counted as much or more than class for recently arriving immigrant groups including Russians, Italians, and Poles, and race/ethnicity was by far the key predictor for these groups and blacks. We also found that these patterns of homophily were clearest at the scale of individual street segment and first-order combinations of segments. They were similar but less distinct at a larger spatial scale. Keywords Segregation, residential space, spatial data Recent research has emphasized the use of individual-level data to understand the social differentiation of neighborhoods. This study of St. Louis in 1930 follows this tradition. It exploits geocoded data from a 100% transcription of the population to examine the bases of neighborhood formation. It explores the extent to which people were sorted into neighbor- hoods on the basis of their race/ethnicity, social class, nativity, and family composition. This Corresponding author: John R Logan, Brown University, Box 1916, Providence, RI 02912, USA. Email: john_logan@brown.edu Environment and Planning B: Urban Analytics and City Science 2018, Vol. 45(6) 1157–1174 ! The Author(s) 2018 Article reuse guidelines: sagepub.com/journals-permissions DOI: 10.1177/2399808318801958 journals.sagepub.com/home/epb