1. A mapping method, comprising: scanning an environment to obtain depth information of environmental obstacles; capturing an image of the environment to generate an image plane; projecting the enviromnental obstacle depth information onto the image plane, so as to obtain a plurality of projection positions; calculating at least one feature vector from a predetermined range around each of the projection positions in the image plane, wherein when the feature vector cannot be calculated from the predetermined range around each of the projection positions, at least an upper feature vector or at least a lower feature vector is calculated from upper or lower image data of each of the projection positions, wherein the upper feature vector or the lower feature vector is calculated according to upper or lower image data in the image plane relative to a vertical axis of each of the projection positions; combining the depth information of environmental obstacles and each of the feature vectors to generate a sub-map for a certain time point; and combining the sub-maps at all time points to generate a map.