Function route_region 

fn route_region(
    step: Step<'_>,
    routes: &RouteGeometries,
    id: RouteId,
) -> Option<GridRect>

A wire’s corridor: the polyline the router solved for it, or — where none is solved — its two endpoints and whatever waypoints it was authored through. The fallback frames the corridor the wire was drawn through rather than the exact path taken, which is what a camera and a ring need.