  The 20m SPOT DEM (Digital Elevation Model) was acquired by the Office of the
Surveyor-General of the Federation (OSGoF) in Nigeria for use in topographic
mapping. A localized assessment of the DEM is needed to validate its stated
accuracies as it is well known that the vertical accuracy of global DEMs varies
in different landscape contexts. Hence, this study assessed the quality of the
DEM in variable land cover types by comparing its heights against 780 Ground
Control Points (GCPs) in Lagos State and the Federal Capital Territory (FCT) of
Nigeria. The pattern of distribution of the height differences was analysed
using spatial autocorrelation analysis, including other accuracy metrics
employed. In the general accuracy assessment, the DEM yielded root mean square
errors of 2.33m in Lagos and 3.69m in the FCT. It was shown that heights over
the bare lands were the most accurately represented on the DEM while heights
over built-up areas are the least accurate at both locations. Despite this, the
SPOT DEM accuracies in the varying land cover types surpassed its stated global
accuracy. While the spatial distribution of low and high height differences in
Lagos State showed clustering, the converse was the case in the FCT. Following
this assessment, it is recommended that the country should extend the
application scope of the DEM in order to exploit its utility to the maximum.
