Employing high resolution satellite images to update urban maps at medium-large scale and its impact in developing countries

The availability of commercial high resolution satellite images has drawn cartographer's attention to utilise them for urban area mapping. Orthorectified images may be used as a map directly or as a support to update existing maps at medium-large scale. Nevertheless, the nominal resolution itself does not guarantee that images are suitable for this specific use: the acquisition geometry and the actual resolution may limit the applicability of this product. In fact, the nominal scale, certified in the ancillary metadata files, does not reflect the actual geometric scale of the image automatically. Furthermore, off-nadir angle and sun elevation angle influence the geometry of the image and the object representation. This has significant effects particularly in urban areas, where urban features and their shadows may mask wide areas. However, the availability of these images may be of crucial importance in developing countries, where maps are lacking or it is difficult to obtain them. In this study an application of Ikonos images to the city of Tangier (Morocco) is developed. The usage of images, the comparison between the orthorectified image and the existing maps of the city and the process of drawing the map are addressed and discussed.