Using Landsat-7 Images to Update Canadian National Topographic Data

Natural Resources Canada's Centre for Topographic Information has a significant collection of topographic data at the 1:50 000 scale. The extent of the Canadian landmass makes it very difficult to update these data on a continuing basis. Following production of national Landsat-7 orthoimages coverage produced in partnership with more than 20 Canadian organisations, a project for updating topographic data using these orthoimages was initiated in June 2001. This article presents the operational constraints related to implementing an updating project of this magnitude (nature of topographic entities, image heterogeneity, size of the territory, production rate, absence of recent ground truth, etc.). Moreover, it describes why production could not be completely automated and why some visual interpretation had to be used.