Enviromental Impact Assessment (EIA) studies of public facilities siting usually address very few alternatives -generally not more than one- and often the choice between these alternatives is not clear, the grounds for their selection being poorly described or even absent from the EIA study. Moreover, EIA studies almost always refer to projects with negative enviromental and social impacts, and yet they are usually approved. This situation gives little legitimacy to the procedure and may be a discredit to the institutional bodies involved in EIA processes. Hence the following work builds on this problem, taking its lead from two main working hypotheses: 1.- by generating alternative sites based upon enviromental information it is likely that more suitable alternatives from enviromental and social points of view will be found; 2.- by generating alternative sites based on social actors'information it is likely that alternatives defensible from the social point of view will be found. It must be noted that those two working hypothesis are conected since enviromental impacts ultimately affect people. In this work an extension of the current EIA process is proposed, to include a formal procedure for the generation of alternatives for siting projects that take into account, environmental amd social dimensions of public facility siting project implementation at the design phase of public siting projects. In the EIA process this corresponds to putting into practice the scoping phase of those processes. Throughout this work a computer tool based on the most up to date theories of information processing is proposed: GIS: as the case technology to manage, process, visualise geo-referenced Information and welcoming spatial analysis tools. MCDA: as the technology embedding the multi-perspectives, multi-agents, multi-dimensions and the non-commensurable nature of information to address environmental issues - a diversity preservation mechanism. GENETIC ALGORITHMS: as intelligent information processors and robust search mechanisms inspired by modern computational paradigms such as the evolutionary computation one - a diversity search mechanism. Moreover, this tool was conceptualised to be accessed by PEOPLE in some kind of social process, and not to be used simply as a technocratic tool. That is the main aim and also the step forward of this work: to study the ways in wich information technology and science can approximate to people. This tool was tested for two case studies: a nuclear waste dump siting problem in the UK and the generation of a route for a complementary itinerary in the centre of Portugal.