Details of the sources used:
ISO 3166-2: Codes for the representation of names of countries and their subdivisions – Part 2: Country subdivision code, defines codes for the principal subdivisions of a country or dependent area. First published in 1998.
World Gazetteer: The World Gazetteer provides a comprehensive set of population data and related statistics.
Federal Information Processing Standards (FIPS): are publicly announced standards developed by the US Federal government for use by all non-military government agencies and by government contractors.
Country Sub-level Sources: