Traditional methods of assessing satellite-derived landcover map accuracy are based on samples. In conditions of inaccessible terrain and lack of up-to-date contextual information, the verification of samples frequently is unfeasible. Such conditions are typical for many applications in developing countries and have been encountered by the authors when mapping the landcover of the region of Manaus in the central Brazilian Amazon Basin. Furthermore, sample-based methods fail to provide information on the spatial distribution of thematic map reliability. This article describes a procedure to derive reliability maps to accompany satellite-derived landcover maps.