Where is the mountain? What is a forest? In our world we find many phenomena, which are difficult to locate or delineate because their meaning is not well defined. Fuzzy set theory represents an alternative approach to classic set theory. Problems that arise from subjectivity, vagueness or ambiguity in linguistic terms require such alternative approaches to model our real imperfect world. This seminar introduces fuzzy set theory in the context of soft computing for spatial decision-making and modeling in GIS and Remote Sensing. We will discuss different examples where the use of fuzzy sets and fuzzy logic operators allows for an extension of the analysis by incorporating concepts of partial and multi-memberships of spatial objects. These examples focus on spatial decision-making, spatial uncertainty assessment, and classification procedures to solve problems in ecological, environmental and socio-economic studies.