Much of the current neighborhood-based research uses variables aggregated on administrative boundaries such as zip codes, census tracts, and block groups. However, other methods using current technological advances in geographic sciences may broaden our ability to explore the spatial concentration of neighborhood factors affecting individuals and groups. This article builds on extant neighborhood-based research methods and proposes using a geographic information system (GIS) to explore a conceptually new method of defining neighborhood boundaries for social measurement. Geospatial factors are important in the formation of neighborhoods, and a GIS can be used to define neighborhood boundaries that account for the spatial factors influencing the natural flow and pattern of neighbor interactions. Georeferenced data from the 2000 U.S. census for a midwestern city are presented to elucidate the potential aggregation problems and theoretical arguments. Moran's I statistics show that administrative boundaries may not be valid aggregate measures of neighborhoods or their effects.