Accuracy assessment of the Portuguese CORINE land cover map

This paper presents the accuracy assessment methodology designed and implemented to validate the Portuguese CORINE Land Cover 2000 (CLC2000) cartography. The procedure is based on the comparison of the land cover database with reference data derived from visual interpretation of aerial photography for sample areas. The sample unit is the land cover polygon, organized within a systematic cluster sampling plan. Each cluster of polygons corresponds to an aerial photography, which allowed a reduction in the number of air photos that had to be acquired by maximizing the number of polygons to inspect in each photo. A multinomial distribution was used to estimate the number of samples. In this validation effort, we computed the overall accuracy, producer's accuracy, and user's accuracy. The CLC2000 for Portugal has an overall thematic accuracy of 82.8, with a confidence interval of 80.5-85.2, and that the majority of the CLC classes are mapped with high accuracy.