Biophysical or ecosystem mapping is built on the principle that vegetation composition and distribution responds in predictable ways to specific abiotic terrain conditions. Terrain (surficial geology) mapping and subsequent stratification into ecosystem units forms the basis for local-scale biophysical mapping. Biophysical mapping is therefore an integrated system of mapping which describes both terrain conditions (surficial material type, slope, landscape position, drainage and permafrost conditions) and ecological factors (vegetation community and structure, and soil moisture and nutrient regimes). The Watson Lake area was selected for a pilot biophysical mapping project because of imminent resource activities in southeast Yukon. Local-scale (1:50 000) biophysical mapping was carried out in the 105A/2 NTS map area during 2004 in cooperation with Yukon Environment, Yukon Geological Survey and Cryogeographic Consulting. Analysis of hard copy 1:40 000-scale aerial photographs was conducted to outline preliminary terrain (surficial geology) and ecosystem units. Four weeks of summer field work was then conducted to ground truth the preliminary aerial photograph interpretation and develop a more detailed ecological classification system for southeast Yukon. Following the field season, the corrected mapping was digitized using stereo-georeferenced high-resolution scanned aerial photographs in Microstation Diap Viewer. Subsequent geographic information system (GIS) manipulation was performed in ArcGIS 9.0. Part of the purpose of the project was to develop a methodology for performing biophysical mapping using these technological tools.