Road geometries may be determined from sparse data by receiving mobile device data points comprising data indicating positions of vehicles having traveled on a roadway of a geographic area, the roadway involving a convergence or divergence of road branches for the roadway. At least one trajectory angle for a particular mobile device data point of the mobile device data points may be determined using at least one trajectory line connecting the particular mobile device data point to an adjacent mobile device data point, and mobile device data points may be grouped based on the trajectory angles.