  Equally as important as the distinction between polygon and attribute was the decision to “vectorize” the scanned images. Scanned images gave “raster” data, that is, data in the form of regular grid points which either do or do not possess a specific property, for instance, the presence of a given vegetation type. Vectorization is the replacement of these point-based structures by lines that are naturally interpreted (such as boundaries of habitat types). What is critical is that these lines can then be joined to form polygons. Raster data can be obtained from a variety of sources including maps and photographs; in the present context what is critical is that raster data can be obtained by remote sensing through satellite imagery from which the distribution of many vegetation and soil types can be inferred. As early as 1989 Running and several collaborators estimated the annual evapotranspiration and net photosynthesis for a 28 ´ 55 sq km region of Montana using a GIS software  package.[97]  The study region was divided into 1.1 ´ 1.1 sq km cells defined by satellite sensor pixel size. The GIS package was used to integrate topographic, soil, vegetation and climatic data from a variety of sources including the results of remote sensing. Ecological assumptions entered into the models that were then used to predict evapotranspiration and net photosynthesis. The results obtained were in fairly good agreement with field data.