Fig. 2. Illustration of the computation of Pf and Pff for a landscape represented by a 3 x 3 grid of pixels. Forest pixels are shaded and nonforest pixels are not shaded. In this example, six of the nine pixels are forested and so Pf equals 6/9 or 0.67. Considering pairs of pixels in cardinal directions, the total number of adjacent pixel pairs is 12, and of these, 11 pairs include at least one forested pixel. Five of those 11 pairs are forest-forest pairs, so Pff equals 5/11 or 0.45.