A compilation of results suggests a predictive character to the relationship overall accuracy (Y ) vs. number of classes (X) with Y = -3.90X + 86.38 (r^2 = 0:63) for Landsat ETM+, and Y = -2.78X + 91:69 for Ikonos (r^2 = 0.82) (Andrefou€et et al., in press).