Cities and urban areas play an important role in fostering influenza transmission, often leading to epidemics and even pandemics. Although there is growing literature on influenza transmission at national and international scales, little attention has been paid to a city scale. This article aims to understand the spatial-temporal transmission of influenza and identify its health risks in the urbanized area of Buffalo, New York. An individual-based spatially explicit model is established to replicate an urban contact network, and simulate influenza epidemics. The resulting epidemic curves and infection intensity maps are used to analyze the transmission dynamics, possible contributing factors, and high-risk places and times. The results indicate that the city-wide transmission of influenza can be described by five stages: local growth, expansion, fast city-wide growth, slow city-wide growth, and fade-out. The places and times associated with higher risk are closely related to spatial heterogeneity in the population, and travel behaviors of individuals. Interestingly, these high-risk places and times are insensitive to where infection sources are introduced. This research suggests that high-risk places can be pre-identified as control targets using census and land use data. In addition, a better understanding on the city-wide travel of individuals is critical for designing proper timelines for influenza control. These suggestions will be valuable for local health agencies as they prepare to combat new waves of H1N1 influenza.