Inspired by his studies in Paris, Ryan Gravel wrote his master's thesis at the Georgia Institute of Technology on his idea of converting Atlanta's abandoned 22-mile-long freight-rail corridor, which encircles the city's urban core, into a "belt line" that would reconnect the city's neighborhoods. After graduation, the idea lingered. Gravel later started Friends of the BeltLine, a non-profit that helped win support to push the project forward.