Curtis E. Woodcock Sucharita Gopal Fuzzy set theory and thematic maps: accuracy assessment and area estimation. 153-172 2000 14 International Journal of Geographical Information Science 2 http://taylorandfrancis.metapress.com/openurl.asp?genre=article&issn=1365-8816&volume=14&issue=2&spage=153 db/journals/gis/gis14.html#WoodcockG00