The pattern detected in any ecological mosaic is a function of scale, and the ecological concept of
spatial scale encompasses both extent and grain (Forman and Godron 1986, Turner et al. 1989,
Wiens 1989). Extent is the overall area encompassed by an investigation or the area included within
the landscape boundary. From a statistical perspective, the spatial extent of an investigation is the
area defining the population we wish to sample. Grain is the size of the individual units of
observation. For example, a fine-grained map might structure information into 1-ha units, whereas a
map with an order of magnitude coarser resolution would have information structured into 10-ha
units (Turner et al. 1989). Extent and grain define the upper and lower limits of resolution of a study
and any inferences about scale-dependency in a system are constrained by the extent and grain of
investigation (Wiens 1989). From a statistical perspective, we cannot extrapolate beyond the
population sampled, nor can we infer differences among objects smaller than the experimental units.
Likewise, in the assessment of landscape pattern, we cannot detect pattern beyond the extent of the
landscape or below the resolution of the grain (Wiens 1989).