ISO 3166-1 alpha-2 is a widely used country code system, along with what three-letter system?
ISO 3166-1 alpha-2 ISO 3166-1 alpha-2 codes are two-letter country codes defined in ISO 3166-1, part of the ISO 3166 standard published by the International Organization for Standardization (ISO), to represent countries, dependent territories, and special areas of geographical interest. They are the most widely used of the country codes published by ISO (the others being alpha-3 and numeric), and are used most prominently for the Internet's country code top-level domains (with a few exceptions). They were first included as part of the ISO 3166 standard in its first edition in 1974.
UN M.49 UN M.49 is a standard for area codes used by the United Nations for statistical purposes, developed and maintained by the United Nations Statistics Division. Each area code is a 3-digit number which can refer to a wide variety of geographical, political, or economic regions, like a continent, a country, or a specific group of developed or developing countries. Codes assigned in the system generally do not change when the country or area's name changes (unlike ISO 3166-1 alpha-2 or ISO 3166-1 alpha-3), but instead change when the territorial extent of the country or area changes significantly, although there have been exceptions to this rule.