Weighting-by-choosing: a weight elicitation method for map overlays

In land suitability assessment, the map overlay technique is often used in conjunction with a weighting scheme. A person first determines parent maps' weights by his perceptions about the importance or relative importance of these maps to land suitability. These weight values are then incorporated i nto the map overlay process. On the resultant overlaid maps, the higher sui tability scores are always assigned to those sites that have better conditi ons on the more important parent maps. Of the two approaches that one can t ake in determining maps' weights, tradeoff weighting is more precise than d irect assessment, but also more difficult to use because it requires greate r cognitive efforts from the users. This article presents a weighting-by-ch oosing method that facilitates the process of making tradeoffs through a se ries of site selection exercises. By using hypothetical reference sites as tangible manipulatives. it transforms an otherwise difficult cognitive task into a simple selection exercise. At present, the method applies to two ma ps at a time, but could potentially be extended to multiple maps. (C) 2001 Elsevier Science B.V. All rights reserved.