Michael Mehaffy shared the following images on the Professional Urbanists Listserv. They are before and after of a hillside slum/favela/informal settlement in Bogota:
As you can see, hand-made, rickety staircases up the slope were replaced by concrete stairs, terraces, and covered escalators. The point is not to say whether bottom-up or top-down planning and development is better than the other, but instead, that they must work together, in a concerted, forward progress towards an end of improved quality of life and opportunity. The locals (bottom-up) obviously identified the problem, the steep slope that the informal settlement organized around. Then, the commonwealth, which has the ability and resources, formalizes the vertical circulation into a more convenient and improved organizing device for the community.
In many ways, this is no different than the Near South neighborhood in Fort Worth, adding their own bike lanes and road diets, only for the city to see the progress and benefit and thus formalize with re-engineered streets based on the center of community the neighborhood started.