This paper examines ways to guide spatial decision making processes by the combined use of geographical information systems (GIS), multi-criteria decision analysis (MCDA) and related decision support systems also called spatial MCDA. Two local-scale case studies were conducted in multi-objective marine and coastal spatial planning problems, one focusing on experimental artificial reef siting in the Mediterranean Sea and one on spatial rearrangement of aquaculture production in the Baltic Sea. In both cases similar analytical frameworks were utilized, yet the applied spatial MCDA techniques were tailored case-specifically according to local characteristics and the nature of the decision problems at hand. In both cases the joint use of GIS and MCDA was able to generate concrete, easily interpretable inputs for decision support via quantification and visualization of decision criteria, trade-offs, alternatives and uncertainty, thus supporting further use of GIS-based spatial decision support tools. Albeit such tools may provide valuable insight to MSP and ICZM, they also come with certain limitations which are commonly related to the quality of the input data and the used valuation criteria in situations that may contain a mixture of subjective and objective information. Based on the empirical findings, the applicability of spatial MCDA in these settings and in marine spatial planning in general is discussed. (C) 2014 Elsevier Ltd. All rights reserved.