1. An image processing system for an aerial photograph, which supports map-making by use of a photographic image, the image processing system comprising: a shadow-angle-analyzing means that obtains the shadow-produced angle between the direction in which a shadow is extended and a predetermined direction, based on the information on the photographic image and the shadow produced from a feature shown in the photographic image; a shadow-extension-ratio-analyzing means that obtains the shadow-extended ratio, which means the ratio of the length of the shadow to the length of the feature, based on the information on the photographic image, the length of the feature, and the shadow produced from the feature shown in the photographic image; a polygon-generating means that generates a polygon by extracting the lines constituting the outline of the feature shown in the photographic image and line-connection-processing these lines; and a shadow-area-extracting means that generates the polygon of the shadow area by extracting the shadow area by use of the information on the shadow-produced angle and the shadow-extended ratio from the polygon generated by the polygon-generating means.