A geographical information system (GIS) is used to combine and analyse data from a existing large-area databases concerning tree growth, plantation management and the environmental characteristics of planted sites in Wales. The databases included the UK Forestry Commission Sub-Compartment Database (SCDB), the Soil Survey and Land Research Centre Land Information System (LandIS), Forestry Commission topographic shelter data, and a digital elevation model for Wales. Regression analysis techniques were employed to estimate yield class models for Sitka spruce [Picea sitchensis] and beech [Fagus sylvatica], which were chosen as representative conifer and broadleaved species. The GIS was then used to extrapolate results and generate maps of predicted yield for the whole of Wales. Models of timber costs and revenues (including subsidies) were then used to convert these results into maps of timber values for use in forest investment planning.