GADM, the Database of Global Administrative Areas, is a high-resolution database of country administrative areas, with a goal of "all countries, at all levels, at any time period."[1] The database has a few export formats, including shapefiles that are used in most common GIS applications [2]. Files formatted for the programming language R are also available, allowing the easy creation of descriptive data plots that include geographical maps.[3][4]
Although it is a public database, GADM has a higher spatial resolution than other free databases [5], and also higher than commercial software such as ArcGIS [6].