Résumé
In the early 1990s, Cambodia was emerging from years of conflict and political instability and was embarking on major reconstruction efforts, particularly in terms of urban planning and development. Historical photographs are crucial for analyzing the city’s landscape prior to the rapid urban expansion of the late 20th and early 21st centuries. We utilized 445 high-resolution aerial photographs of Phnom Penh from 1993, taken by the French National Geographic Institute (IGN) and digitized in 2023 through the Khmer Aerial Photographic Archive (KAPA) Project. These images were orthorectified using Agisoft Metashape Profes- sional software, with ground control points collected in 1993, and a Digital Terrain Model from ALOS to correct the geometry. The study focuses on Phnom Penh’s extent in 1993, covering five districts: Chamkarmon, 7 Makara, Daun Penh, Toul Kok, and the southern part of Reussey Keo. An advanced object-based image analysis (OBIA) was realized with eCognition Developer to detect green areas within the city. A vector layer of buildings from APUR (Atelier Parisien de Urbanisme) helped differentiate vegetation from buildings. Ap- plying OBIA with a multiresolution segmentation to historical photos allowed the detection of vegetation. Vegetation in Phnom Penh was categorized into street trees and urban green areas. Street trees covered the largest extent with 535 hectares, while urban green areas spanned about 60 hectares across the five districts in 1993. The historical aerial imagery provides valuable data for assessing the evolution of green spaces. The study’s findings offer insights into urban development patterns, environmental degradation, and the preservation of green spaces in Phnom Penh over the decades. This research supports informed decision- making in urban planning and promotes sustainable management of urban environments in Cambodia and other rapidly urbanizing regions.