cf. city flows is a comparative visualization environment of urban bike mobility designed to help citizens casually analyze bike-sharing systems in the context of a public exhibition space. Three high-resolution screens show the space of flows in New York City, Berlin and London. By showing the flow of multiple cities side by side, we can compare their extent and dynamics. Tracing urban movements accentuates different urban structures and enables us to observe similarities and differences in various bike-sharing systems. cf. city flows applies established mapping and visualization techniques within a highly aestheticized framework in order to encourage visitors to engage with the spatiotemporal complexity of urban mobility. Through our visualizations, we can better understand the pulse of urban mobility and create portraits of a city defined by its transient dynamics.