COMBINING GIS AND FUZZY SET TO IMPROVE MULTI CRITERIA SPATIAL DECISION MAKING Delavar M.R. 1 , M.R. Malek 2 , S. Saeedi 1 and A. Tayyebi 1 1 Center of Excellence in Geomatics Eng. and Disaster Management, Dept. of Surveying and Geomatics Eng., Colledge of Eng., University of Tehran, Tehran, Iran [mdelavar, ssaeedi, atayyebi]@ut.ac.ir 2 Factualy of Geodesy and Geomatic, KNToosi, Industrial university, Tehran, Irahn malek@ncc.neda.net.ir Abstract. One of the most fertile GIS development areas is integrating multiple criteria decision models into GIS query mechanisms using information from different layers. Although this problem is very relevant in practice, there are few methods available that can handle the complex criteria and the uncertainties of the problem solving aspects. However, in most complex real world decision making processes, information layers, decision criteria and their interrelations are often complex and vague. This paper focuses on a framework based on integration of GIS and multi-criteria decision making (MCDM) by implementing the fuzzy set theory as a method for representing the performance of decision alternatives on evaluation criteria and fuzzy analytical network process (Fuzzy-ANP) methods for criteria weighting, capturing geospatial preferences and decision rules. The case study undertaken in this research includes investigation of certain criteria used in selecting the public multi-level parking sites in a part of Tehran metropolitan area. Effective parameters in suitable site selection for public parking such as physical site features, absorbing excursion spaces, traffic situation, intermodal transit and pedestrian related issues, economic parameters and legal restrictions have been considered. This paper successfully demonstrates that the proposed method has the ability to include a number of geospatial data and constraints simultaneously to improve decision-making using the GIS-based fuzzy logic approach. Key Words: ANP, Fuzzy Set Theory, GIS, Spatial Multi Criteria Decision Analysis, Parking Site Selection 1. Introduction Decision making is a selection of alternative course of action, in many fields, based on both the spatial and non-spatial information. Multi criteria decision making (MCDM) techniques can be used to identify a single most preferred option, to rank options, to list a limited number of options for subsequent detailed evaluation, or to distinguish acceptable from unacceptable possibilities [4]. Since 80% of data used by decision makers is related geo-spatially [17], spatial decision making may provide superior framework in variety of decision making situations. Nowadays as geo-spatial information systems (GIS) are becoming more widely used for making critical decisions in many disciplines [1], more sophisticated approaches heightens in spatial decision making. Especially multiple criteria