The aim of this study is to develop a methodology for using Geographic Information Systems (GIS) spatial analysis in the development of a floating offshore wind farm. When you plan a floating offshore wind farm it is very important to determine the areas where wind resource is high, which will produce good economic results in terms of the feasibility of the farm. However, the present paper analyses how some restrictions (environmental areas, navigation restricted areas, depth, ports, shipyards, etc.) affect to the floating offshore wind farm. The tool developed allows increasing the quantity of these restrictions as the user needs. The procedure has been considered for the Galician area (North-West of Spain), a region that has experience in onshore wind. Therefore, the GIS tool analyses the site selection for a floating offshore wind farm.