The successive topographic maps of the French IGN show the urbanization of the Parisian suburbs over the decades near the stations of the suburban lines. In the region, especially south of the capital, these lines follow the bottom of the valleys because the steam traction did not support the steep gradients: the urbanization of the trays takes place later with the advent of the automobile for the general public during the second half of the 20th century. The automobiles allowed people either to go directly to work, or to live at a distance from the station, where the land prices and rents are lower than in the immediate vicinity of the stations.