GADM is a spatial database of the location of the world's administrative areas (or adminstrative boundaries) for use in GIS and similar software. Administrative areas in this database are countries and lower level subdivisions such as provinces, departments, bibhag, bundeslander, daerah istimewa, fivondronana, krong, landsvæðun, opština, sous-préfectures, counties, and thana. GADM describes where these administrative areas are (the "spatial features"), and for each area it provides some attributes, such as the name and variant names.
The current version is 2.0 (January 2012)
Compared to Version 1, GADM Version 2 has, among other things, more detailed data for Belgium, Bosnia and Herzegovina, Croatia, Cuba, Dominican Republic, Luxembourg, Estonia, France, Hungary, Nepal, Turkey, Switzerland, Syria, Uzbekistan, and Venezuela. Sudan was split in two and a few Caribbean islands were split or rearranged. With only a few exceptions, the second level subdivision has now been mapped for all countries (see these maps by level of subdivision). The current version of GADM delimits 556,049 administrative areas (or 218,238 if you count only the lowest level for each country).
The data are available as shapefile, ESRI geodatabase, RData, and Google Earth kmz format. Shapefiles can be used for most mapping and "GIS" software. You can download a free program such as Q-GIS or DIVA-GIS. The RData files can be used in R with the 'sp' package loaded.
Our goal is to map the administrative areas of all countries, at all levels. We use a high spatial resolution, and of a extensive set of attributes for each spatial feature. This is a never ending project, but we are happy to share what we have so far. Please contribute in whatever way you can by sending us a message to point out errors, or even better, to send an improved file for a country of your interest.
Here are links to other sources of administrative area data and related information.