1. A method, comprising: performing, by one or more computing devices: accessing footprint data for one or more structures within a map region; identifying, from a three-dimensional data set corresponding to the map region and based on the footprint data for a structure of the one or more structures within the map region, a plurality of points on a roof of the structure; calculating, based on the plurality of points on the roof of the structure, a plurality of normals; generating a two-dimensional representation comprising a corresponding pair of geometric coordinates for each of the plurality of normals, each pair of geometric coordinates determined based at least in part on a transformation of corresponding three-dimensional coordinates of the corresponding normal for the plurality of normals; identifying, based at least in part on the two-dimensional representation of the plurality of normals, a plurality of groups of normals from among the plurality of normals; identifying, based on different respective groups of normals within the plurality of groups of normals, different respective planes of the roof; and determining a parameter set for the roof of the structure based on parameter values describing the different respective planes of the roof that have been identified based on the different groups of normals.