±12 hours. In theory, ships are supposed to adopt the standard time of a country if they are within its territorial waters within of land, then revert to international time zones (15° wide pole-to-pole gores) as soon as they leave. In practice, ships use these time zones only for radio communication and similar purposes. For internal (within-ship) purposes, such as work and meal hours, ships use a time zone of their own choosing. Cartographic practice and convention The IDL on the map in this article and all other maps is based on the de facto line and is an artificial construct of cartographers, as the precise course of the line in international waters is arbitrary. The IDL does not extend into Antarctica on the world time zone maps by the United States Central Intelligence Agency (CIA) or the United Kingdom's His Majesty's Nautical Almanac Office (HMNAO). The IDL on modern CIA maps now reflects the most recent shifts in the IDL (see below). The current HMNAO map does not draw the IDL in conformity with recent shifts in the IDL; it draws a line virtually identical to that adopted by the UK's Hydrographic Office about 1900. Instead, HMNAO labels island groups with their time zones, which do reflect the most recent IDL shifts. This approach is consistent with the principle of national and nautical time zones: the islands of eastern Kiribati are actually "islands" of Asian date (west side of IDL) in a sea of American date (east side of IDL). Similarly, the western Aleutian Islands are islands of American date in a sea of Asian date. No international organization, nor any treaty between nations, has fixed the IDL drawn by cartographers: the 1884 International Meridian Conference explicitly refused to propose or agree to any time zones, stating that they were outside its purview. The conference resolved that the Universal Day, midnight-to-midnight Greenwich Mean Time (now redefined and updated as Coordinated Universal Time, or UTC), which it did agree to, "shall not interfere with the use of local or standard time where desirable". From this comes the utility and importance of UTC or "Z" ("Zulu") time: it permits a single universal reference for time that is valid for all points on the globe at the same moment. Historic alterations Philippines (1521 and 1844) Ferdinand Magellan claimed the Philippines for Spain on Saturday, , having sailed westwards from Seville across the