The species distribution maps, sometimes referred to as ‘limits of distribution’ or ‘field guide’ maps, aim to provide the current known distribution of the species within its native range. The limits of distribution can be determined by using known occurrences of the species, along with the knowledge of habitat preferences, remaining suitable habitat, elevation limited, and other expert knowledge of the species and its range. In most cases the range is depicted as polygons. A polygon displaying the limits of a species distribution is essentially meant to communicate that the species probably occurs within this polygon, but it does not mean that it is distributed equally within that polygon or occurs everywhere within that polygon. The IUCN Red List of Threatened Species uses spatial data for the mapping of species. The spatial data is created in shapefiles and compiles of a standardise format of attributes. Each shapefile must contain taxonomic information, and contain information on the distribution status, sources and other details (see metadata document). Below are some of the IUCN Red List Tools, basedata and example polygon shapefiles. The following documents and tools are available to help users to find their way around species mapping of IUCN Red List assessments: Esri – GIS Mapping Software, links to ArcGIS for Desktop free trial, Esri Resource Center for support, maps and data and training. WWF Conservation Science Data and Tools – Data for Marine, Freshwater and Terrestrial Ecoregions and other data sets. Source.