The urban forest is being recognized for not only aesthetic benefits but for carbon storage, air filtration, noise reduction and wildlife habitat. This acknowledgment has resulted in actions supporting the urban forest ranging from federal funding of state urban forestry programs to grassroot urban tree planting/advocacy groups. As with any forestry related project, there is an interest to know how much, and where the vegetation exists. Landsat satellite imagery (Thematic Mapper) has been proved effective for mapping the density (crown closure) of non-urban forests. This project uses this same imagery to map the density of the urban forest within the City of Portland, Oregon. In a second phase, this map along with other mapped information will form a model of the city for the purpose of locating areas that could sustain more vegetation. (This work is currently in progress and to date has produced a preliminary map of urban forest density using the imagery.) Computer image processing of the satellite imagery provides the basis for a city-wide map of urban forest density. Color infrared aerial photos supplies the initial ground truth for vegetation density and to also distinguish among trees, shrubs and grass. Particular emphasis is put on residential lands containing yard and street trees as mapping of urban natural areas (patches of remaining forest and meadows) has already been accomplished by other mapping projects. The final map of vegetation density will be a digital map ready for use within a geographic information sysem (GIS). This will start the second phase of the project where a more representative model of the urban environment will be constructed by joining the vegetation map with other GIS maps of population streets, tax parcels and zoning. The forest density map by itself will certainly show areas that are below average density. However, by making spatial correlations between the forest density map and population density, street density, tax parcel density and zoning, it is hoped to improve the accuracy in showing areas that could support more vegetation.