  Urban areas serve as melting pots of people with diverse socioeconomic
backgrounds, who may not only be segregated but have characteristic mobility
patterns in the city. While mobility is driven by individual needs and
preferences, the specific choice of venues to visit is usually constrained by
the socioeconomic status of people. The complex interplay between people and
places they visit, given their personal attributes and homophily leaning, is a
key mechanism behind the emergence of socioeconomic stratification patterns
ultimately leading to urban segregation at large. Here we investigate mixing
patterns of mobility in the twenty largest cities of the United States by
coupling individual check-in data from the social location platform Foursquare
with census information from the American Community Survey. We find strong
signs of stratification indicating that people mostly visit places in their own
socioeconomic class, occasionally visiting locations from higher classes. The
intensity of this `upwards bias' increases with socioeconomic status and
correlates with standard measures of racial residential segregation. Our
results indicate an even stronger socioeconomic segregation in individual
mobility than one would expect from system-level distributions, shedding
further light on uneven mobility mixing patterns in cities.
