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.
List of NATO country codes This is the list of NATO country codes. Up to and including the seventh edition of STANAG 1059, these were two-letter codes (digrams). The eighth edition, promulgated February 19, 2004, and effective April 1, 2004, replaced all codes with new ones based on the ISO 3166-1 alpha-2 codes. Additional codes cover gaps in the ISO coverage, deal with the imaginary countries used for exercise purposes, and designate large geographical groupings and water bodies (ranging from oceans to rivers). It consists of two-letter codes for geographical entities, four-letter codes for subdivisions, and lists the ISO three-letter codes for reference. The digrams match the FIPS 10-4 codes with a few exceptions.