ABSTRACT
Error and uncertainty have always been a feature of cartographic information so it hardly surprising that these aspects are also present in digital versions of analogue maps. Neither should it be imagined that any map-related spatial data exist which are error-free. Errors and uncertainty are facts of life in all information systems. There are many different causes of uncertainty and those explicitly due to GIS-based manipulations of mappable information are merely a more recent problem. However, it is also obvious that GIS has the potential to dramatically increase both the magnitude and importance of errors in spatial databases. Urgent action is needed to minimise the potential worst case consequences and also to provide a methodology for coping with the effects of processing uncertain data. Yet as Burrough (1986) points out ªIt is remarkable that there have been so few studies on the whole problem of residual variation and how errors arise, or are created and propagated in geographical information processing, and what the effects of these errors might be on the results of the studies madeº (page 103). Indeed, there is a remarkable lack of information about the level of errors in map and remotely sensed data and, there are seemingly no available tools for measuring error in the outputs, and no methodology for assessing their significance.
