Reducing positional error in spatio-temporal analyses

A frequent method used to assess land use / land cover (LULC) change is the comparison (overlay) of digital maps of an area within a geographic information system (GIS). However, positional errors of the maps involved in the comparison tend to create “false” change polygons and to overestimate LULC change. In this work, a simple method to improve change estimates by detecting and correcting erroneous changes resulting from positional errors is presented. In this approach, the boundary uncertainty is managed using the epsilon band which encloses a confidence region with a specific probability of including the true location of the boundary. In order to test the method, a map of change was first generated through the overlay of two digital versions of the same analogical cartography. False changes resulting from both positional (digitizing) and thematic (labelling) errors were quantified. Finally, the method was applied to a LULC change monitoring project in a region of South-eastern Mexico, which has been undergoing important land cover changes during the past decades. In both cases, the method allowed a significant reduction of erroneous changes due to positional errors. Due to the complexity of error modelling approaches, such simple methods are likely to be the most useful in the context of practical projects aimed at assessing LULC change.