GPS and GIS to assess the accuracy of land cover maps in mountain areas

The creation of thematic maps by photointerpretation of aerial photographs of non-flat areas should rely on orthocorrected images. When the application of orthocorrection is not possible (lack of elevation data or suitable software) the question is posed as to which alternative method minimises the effect of relief in the displacement of the category boundaries. The work described here applies a method for assessing the spatial accuracy of linear features in thematic maps to assess the performances, in mountain areas, of two mapping methods which do not include orthocorrection. The test was performed on two study areas in order to determine the best method for producing land cover maps on other 9 study areas. The first method included the rectification of aerial photographs with a rubber sheet transformation, on-screen photointerpretation and digitising. The second method included traditional photointerpretation, tracing the boundaries on base maps and digitising. GPS in kinematic differential mode was used to collect reference data for the assessment of spatial accuracy. The assessment showed that the second method resulted more accurate in both study areas. Transactions on Information and Communications Technologies vol 18, © 1998 WIT Press, www.witpress.com, ISSN 1743-3517