Patch-based transitions are considerably more difficult because of the task of patch identification. A patch (or cluster) is a group of contiguous grid cells with identical landscape condition labels. The North-East-West-South (NEWS) Neighbor Rule [2] was used to define adjacency. The patch-identification algorithm in Figure 4 is used by the GRASS program r.clump and was incorporated into LUCAS because of the availability of its source code and its relatively meager memory usage. It is a two-pass algorithm which requires only the current and previous rows to be in memory at one time. The transition is calculated in the same manner as in the pixel-based model when a new patch is created and its value is passed on to the other members of the current patch.
