A cell monolayer cultured on an anisotropic substrate may undergo a flocking transition in which cells migrate collectively in wide, bidirectional, “lanes”. If the substrate is not only anisotropic but also locally asymmetric, thanks to a ratchet-like shape of the guiding cue, a new mode of collective migration perpendicular to the lines develops. The present project aims at understanding this rectification by massive tracking of the cells using machine-learning-based strategies.