source dataset Z*, and co-located values from an independent source
of higher accuracy (i.e. check points) Z, were calculated. When a small
data set was available (as a consequence of the limited number of
check points available for 1969 models) the mean absolute error
(MAEZ) was used instead of RMSE due to its smaller sensitivity to large
errors. Since the application of these statistics assumes that data
follow the Gaussian distribution, residuals (ΔZ) were tested for
normality. The normality assumption was not rejected (p>0.2–0.65)
for any of the data sets inspected. Consequently, RMSEZ (as well as
MAEZ and MEZ) were used as indicators of elevation accuracy of DEMs
in spite of some limitations pointed out by several authors (e.g.
Kyriakidis et al., 1999; Heuvelink, 2002; Wechsler, 2007).