  Social connections that span across diverse urban neighborhoods can help
individual prosperity by mobilizing social capital in cities. Yet, how the
detailed spatial structure of social capital varies in lower- and higher-income
urban neighborhoods is less understood. This paper demonstrates that the social
capital measured on social networks is spatially more concentrated for
residents of lower-income neighborhoods than for residents of higher-income
neighborhoods. We map the micro-geography of individual online social
connections in the 50 largest metropolitan areas of the US using a large-scale
geolocalized Twitter dataset. We then analyze the spatial dimension of
individual social capital by the share of friends, closure, and share of
supported ties within circles of short distance radiuses (1, 5, and 10~km)
around users' home location. We compare residents from below-median income
neighborhoods with above-median income neighborhoods, and find that users
living in relatively poorer neighborhoods have a significantly higher share of
connections in close proximity. Moreover, their network is more cohesive and
supported within a short distance from their home. These patterns prevail
across the 50 largest US metropolitan areas with only a few exceptions. The
found disparities in the micro-geographic concentration of social capital can
feed segregation and income inequality within cities harming social circles of
low-income residents.
