SIOSE, Spanish acronym standing for Land Cover and Use Information System of Spain, is the most detailed Geographic Information System ever created in Spain about land cover and land use. This GIS gives objective information, photo-interpreted from aerial and satellite imagery, describing the different land covers and land uses. Since SIOSE gathers a big deal of information (more than 157.000 different polygons just in the Land of Valencia), the quantity of possible researches coming from it is huge and ranging from environmental and biodiversity subjects to agricultural or urban areas topics. These possible researches would be especially appropriate on a local level, since SIOSE has a very detailed and precise information, whereas on a regional or national level, it is better to use CORINE land cover, that for many years has been the reference GIS for land use researches in Valencia and Spain. In this paper we will compare CORINE and SIOSE in order to sort out the main differences between them, both as regards land use classification and the different map scales in which each of them ought to be used.