Familiarity with common terms from landscape ecology and geographic information systems helps to better understand the LUCAS model. The spatially explicit multidisciplinary data is stored in raster maps. Raster maps, also known as data layers, are matrices of integers. Each entry in the matrix is called a grid cell or pixel and corresponds to the value of an attribute, such as elevation, for a particular parcel of land. Contiguous pixels with the same value are called patches or clusters. Many other geographic terms are discussed in Section 2 in which GRASS is introduced.
The concept of transition is central to the LUCAS model. A transition is a change, usually in land cover, from a given state to a new state as dictated by the land-use scenario. Transition probabilities are the probabilities of a transition occurring for a particular grid cell. The generation of transition probabilities is discussed in Section 3. A scenario is a predefined land management policy. LUCAS defines many scenarios for each watershed it simulates. Two watersheds, distinct geographic regions, are currently supported: the LTRB and the Hoh River on the Olympic Peninsula.
As discussed in Section 3, a stochastic simulation requires multiple replicates, repeated trials, to statistically verify the simulation. Usually many time steps, five year intervals, are simulated for each replicate to model change over an extended period of time.