Distinction between regional and local facies maps is commonly based on map scale, area covered, and tightness of control. An alternative manner of distinguishing between regional and local effects on maps of any scale can be based on the relative areal persistence of regional trends in contrast to the lesser areal persistence of local fluctuations. The regional trends reflect relatively broad tectono-environmental controls on sedimentation, whereas the more local fluctuations may be due to smaller-scale environmental, structural, or pre-existing topographic effects.

Principles underlying practical ways of separating regional and local effects on maps of any scale are illustrated by conventional graphic methods adapted from geophysical practice, as well as by analytic methods that permit more detailed study of regional gradients. Examples of analyzed facies maps suggest that the separation of these effects may afford a basis for sounder interpretation of facies maps in general, as well as indicating local areas where economically important departures may occur from the regional facies patterns.