Vélotropolis is a prototype supply-demand visualization tool designed with the aim to quickly highlight the gap in the provision of bike lanes across the city. Using available origin-destination data of shared bike systems, the tool derives the theoretical shortest travel path for each journey and overlays its trajectory on the city map. The aggregated layers of cycling trajectories, in turn, form a visual “demand density” on the road network, which can then be easily compared to the presence of bike lanes based on data typically made available through city governments’ open data platforms. The user can also integrate other information, such as the locations of bike accidents as a way to further inform the prioritization of investment on bike lanes in particular areas of the city.