This talk brings together three papers that use GPS mobility data to study how a city’s spatial configuration and size shape mobility and social outcomes. I begin by showing that Americans routinely travel far from home—only 14% of daily consumption trips occur within a short walk. The fact that most trips are long raises environmental concerns since expanding cities may face increasing congestion, pollution, and other transportation-related challenges. In order to explore the relationship between city size and mobility, I analyze travel times across cities of different sizes and document that the total amount of time individuals spend travelling per day remains fairly constant regardless of city size. This regularity raises a key question: How do cities adapt to accommodate growing populations while maintaining similar travel times? Our findings show that urban areas adjust through densification, the development of multiple centers, and investments in faster infrastructure. Finally, I examine how these adaptations affect segregation. While trips far from home generally increase opportunities for interaction, their ability to reduce segregation depends on a city’s spatial layout—less spatially clustered cities promote integration more effectively than highly clustered ones.