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The study of spatial distribution of forest changes tin the northern forests of Iran
4. Preparing digital elevation model (DEM) After extracting contour lines from the 3D digital maps, a precise digital elevation model having a spatial resolution of 30 meters was created for each watershed basin separately. 5. Preparing elevation, slope and aspect maps Slope and aspect maps were achieved using digital elevation model. Elevation classes map considering 100 meters classes was obtained through the classification of digital elevation model. Slope classes map was achieved by classifying the slope map into 6 classes including 0-20%, 20-40%, 40-70%, 70-100%, 100-150% and >150%. Aspect map was also classified into four main geographical aspects. 6. Preparing distance class maps, considering the distance from roads and residential areas Distance from roads and residential areas were the two other important data layers. Roads and residential areas layers were extracted from digital maps dating 2001 in the Microstation software and later these maps were converted from vector to raster format. Distance from roads and residential areas maps were prepared for each watershed basin separately. These maps were then classified considering 200 meters classes. All of the mentioned maps as geographical data layers stored in raster-based Idrisi software. The resolution of all of the maps was 30m* 30m. Each of these classified maps was multiplied by forest decrease map to determine the role of them in reducing the area of the forest in each watershed basin.  Fig. 2. The forest map dated 1967 (a), the forest map dated 1994 (b) and The forest change map in this period (c). |