MAP ACCURACY ASSESSMENT ISSUES WHEN USING AN OBJECT-ORIENTED APPROACH

When a land covermap is created using an Object Based Image Analysis (OBIA) approach, the pixels are grouped so that within-segment variances are less than between-segment variances and the thresholds for both minimum size and maximum variability of the segments are defined by the analyst creating the map. Therefore, the segments are generally not all the same size and are dependent on the properties of the image. In order to validate maps created using an OBIA approach, the reference sample units should be the same as the segments (i.e. polygons), rather than pixels, so that the units are directly comparable to the map segments. However, unlike in more traditional pixelbased mapping techniques, each unit will have a unique size, which should be accounted for in the assessment process. Therefore, an error matrix that incorporates the reference unit area into each cell is proposed for reporting the thematic accuracy of a map created using an OBIA approach. This study reports the new area-based error matrix in conjunction with the traditional error matrix, to provide a more complete representation of an accuracy of a land covermap created using an OBIA approach.