1. A machine-implemented method for generating a road network based on satellite imagery, the method comprising: obtaining plural pixels corresponding to satellite imagery of a region; calculating, for each of the plural pixels, a probability value corresponding to the probability that the pixel belongs within the road network; forming a grayscale image based on the calculated probability values; producing plural curves based on the grayscale image, wherein the producing of each curve comprises: positioning a shape on the grayscale image so that an average intensity of the grayscale image covered by the shape exceeds a preset threshold; moving the shape about the grayscale image while the average intensity is maintained; tracking the movement of the shape to produce the curve; and generating a planar-connected graph by connecting at least portions of the plural curves, wherein the planar-connected graph corresponds to the road network.