note 1: archipelago of 55 islands; Diego Garcia, the largest and southernmost island, occupies a strategic location in the central Indian Ocean; the island is the site of a joint US-UK military facility

note 2: Diego Garcia is the only inhabited island of the BIOT and one of only two British territories where traffic drives on the right, the other being Gibraltar

note 1: second-largest country in world (after Russia) and largest in the Americas; strategic location between Russia and US via north polar route; approximately 90% of the population is concentrated within 160 km (100 mi) of the US border

note 2: Canada has more fresh water than any other country and almost 9% of Canadian territory is water; Canada has at least 2 million and possibly over 3 million lakes - that is more than all other countries combined

note 1: Chad is the largest of Africa's 16 landlocked countries

note 2: not long ago - geologically speaking - what is today the Sahara was green savannah teeming with wildlife; during the African Humid Period, roughly 11,000 to 5,000 years ago, a vibrant animal community, including elephants, giraffes, hippos, and antelope lived there; the last remnant of the "Green Sahara" exists in the Lakes of Ounianga (oo-nee-ahn-ga) in northern Chad, a series of 18 interconnected freshwater, saline, and hypersaline lakes now protected as a World Heritage site

note 3: Lake Chad, the most significant water body in the Sahel, is a remnant of a former inland sea, paleolake Mega-Chad; at its greatest extent, sometime before 5000 B.C., Lake Mega-Chad was the largest of four Saharan paleolakes that existed during the African Humid Period; it covered an area of about 400,000 sq km (150,000 sq mi), roughly the size of today's Caspian Sea

note 1: the longest north-south trending country in the world, extending across 39 degrees of latitude; strategic location relative to sea lanes between the Atlantic and Pacific Oceans (Strait of Magellan, Beagle Channel, Drake Passage)

note 2: Chile is one of the countries along the Ring of Fire, a belt of active volcanoes and earthquake epicenters bordering the Pacific Ocean; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire

note 3: the Atacama Desert - the driest desert in the world - spreads across the northern part of the country; Ojos del Salado (6,893 m) in the Atacama Desert is the highest active volcano in the world, Chile's tallest mountain, and the second highest in the Western Hemisphere and the Southern Hemisphere - its small crater lake (at 6,390 m) is the world's highest lake

note 1: second largest country in Africa (after Algeria) and largest country in Sub-Saharan Africa; straddles the equator; dense tropical rain forest in central river basin and eastern highlands; the narrow strip of land that controls the lower Congo River is the DRC's only outlet to the South Atlantic Ocean

note 2: because of its speed, cataracts, rapids, and turbulence the Congo River, most of which flows through the DRC, has never been accurately measured along much of its length; nonetheless, it is conceded to be the deepest river in the world; estimates of its greatest depth vary between 220 and 250 meters

Curacao is a part of the Windward Islands (southern) group in the Lesser Antilles

islands' component is widely scattered across remote locations in the southern Indian Ocean

Bassas da India (Iles Eparses): atoll is a circular reef atop a long-extinct, submerged volcano;

Europa Island and Juan de Nova Island (Iles Eparses): wildlife sanctuary for seabirds and sea turtles;

Glorioso Island (Iles Eparses): islands and rocks are surrounded by an extensive reef system;

Tromelin Island (Iles Eparses): climatologically important location for forecasting cyclones in the western Indian Ocean; wildlife sanctuary (seabirds, tortoises)

note 1: strategic location on Strait of Gibraltar that links the North Atlantic Ocean and Mediterranean Sea

note 2: one of only two British territories where traffic drives on the right, the other being the island of Diego Garcia in the British Indian Ocean Territory

note 1: despite having both eastern and western coastlines (Caribbean Sea and Pacific Ocean respectively), there are no natural harbors on the west coast

note 2: Guatemala is one of the countries along the Ring of Fire, a belt of active volcanoes and earthquake epicenters bordering the Pacific Ocean; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire

note 1: according to Indonesia's National Coordinating Agency for Survey and Mapping, the total number of islands in the archipelago is 13,466, of which 922 are permanently inhabited (Indonesia is the world's largest country comprised solely of islands); the country straddles the equator and occupies a strategic location astride or along major sea lanes from the Indian Ocean to the Pacific Ocean

note 2: Indonesia is one of the countries along the Ring of Fire, a belt of active volcanoes and earthquake epicenters bordering the Pacific Ocean; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire; 80% of tsunamis, caused by volcanic or seismic events, occur within the "Pacific Ring of Fire"

note 3: despite having the fourth largest population in the world, Indonesia is the most heavily forested region on earth after the Amazon

note 1: strategic location in northeast Asia; composed of four main islands - from north: Hokkaido, Honshu (the largest and most populous), Shikoku, and Kyushu (the "Home Islands") - and 6,848 smaller islands and islets

note 2: Japan annually records the most earthquakes in the world; it is one of the countries along the Ring of Fire, a belt of active volcanoes and earthquake epicenters bordering the Pacific Ocean; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire

note 1: strategic location on southern border of the US; Mexico is one of the countries along the Ring of Fire, a belt of active volcanoes and earthquake epicenters bordering the Pacific Ocean; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire

note 2: some of the world's most important food crops were first domesticated in Mexico; the "Three Sisters" companion plants - winter squash, maize (corn), and climbing beans - served as the main agricultural crops for various North American Indian groups; all three apparently originated in Mexico but then were widely disseminated through much of North America; avocado, amaranth, and chili peppers also emanate from Mexico, as does vanilla, the world's most popular aroma and flavor spice; although cherry tomatoes originated in Ecuador, their domestication in Mexico transformed them into the larger modern tomato

note 3: the Sac Actun cave system at 348 km (216 mi) is the longest underwater cave in the world and the second longest cave worldwide, after Mammoth Cave in the United States (see "Geography - note" under United States)

note 4: the prominent Yucatan Peninsula that divides the Gulf of Mexico from the Caribbean Sea is shared by Mexico, Guatemala, and Belize; just on the northern coast of Yucatan, near the town of Chicxulub (pronounce cheek-sha-loob), lie the remnants of a massive crater (some 150 km in diameter and extending well out into the Gulf of Mexico); formed by an asteroid or comet when it struck the earth 66 million years ago, the impact is now widely accepted as initiating a worldwide climate disruption that caused a mass extinction of 75% of all the earth's plant and animal species - including the non-avian dinosaurs

note 1: consists of two main islands and a number of smaller islands; South Island, the larger main island, is the 12th largest island in the world and is divided along its length by the Southern Alps; North Island is the 14th largest island in the world and is not as mountainous, but it is marked by volcanism

note 2: New Zealand lies along the Ring of Fire, a belt of active volcanoes and earthquake epicenters bordering the Pacific Ocean; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire

note 3: almost 90% of the population lives in cities and over three-quarters on North Island; Wellington is the southernmost national capital in the world

note 1: shares island of New Guinea with Indonesia; generally east-west trending highlands break up New Guinea into diverse ecoregions; one of world's largest swamps along southwest coast

note 2: two major food crops apparently developed on the island of New Guinea: bananas and sugarcane

note 3: Papua New Guinea is one of the countries along the Ring of Fire, a belt of active volcanoes and earthquake epicenters bordering the Pacific Ocean; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire

note 1: shares control of Lago Titicaca, world's highest navigable lake, with Bolivia; a remote slope of Nevado Mismi, a 5,316 m peak, is the ultimate source of the Amazon River

note 2: Peru is one of the countries along the Ring of Fire, a belt of active volcanoes and earthquake epicenters bordering the Pacific Ocean; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire

note 3: on 19 February 1600, Mount Huaynaputina in the southern Peruvian Andes erupted in the largest volcanic explosion in South America in historical times; intermittent eruptions lasted until 5 March 1600 and pumped an estimated 16 to 32 million metric tons of particulates into the atmosphere reducing the amount of sunlight reaching the earth's surface and affecting weather worldwide; over the next two and a half years, millions died around the globe in famines from bitterly cold winters, cool summers, and the loss of crops and animals

note 4: the southern regions of Peru and the extreme northwestern part of Bolivia are considered to be the place of origin for the common potato

note 1: for decades, the Philippine archipelago was reported as having 7,107 islands; in 2016, the national mapping authority reported that hundreds of new islands had been discovered and increased the number of islands to 7,641 - though not all of the new islands have been verified; the country is favorably located in relation to many of Southeast Asia's main water bodies: the South China Sea, Philippine Sea, Sulu Sea, Celebes Sea, and Luzon Strait

note 2: Philippines is one of the countries along the Ring of Fire, a belt of active volcanoes and earthquake epicenters bordering the Pacific Ocean; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire

note 3: the Philippines sits astride the Pacific typhoon belt and an average of 9 typhoons make landfall on the islands each year - with about 5 of these being destructive; the country is the most exposed in the world to tropical storms

note 1: largest country in the world in terms of area but unfavorably located in relation to major sea lanes of the world; despite its size, much of the country lacks proper soils and climates (either too cold or too dry) for agriculture

note 2: Russia's far east, particularly the Kamchatka Peninsula, lies along the Ring of Fire, a belt of active volcanoes and earthquake epicenters bordering the Pacific Ocean; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire

note 3: Mount El'brus is Europe's tallest peak; Lake Baikal, the deepest lake in the world, is estimated to hold one fifth of the world's fresh surface water

note 4: Kaliningrad oblast is an exclave annexed from Germany following World War II (it was formerly part of East Prussia); its capital city of Kaliningrad - formerly Koenigsberg - is the only Baltic port in Russia that remains ice free in the winter

the northern border is shared with the French overseas collectivity of Saint Martin; together, these two entities make up the smallest landmass in the world shared by two self-governing states

note 1: world's third-largest country by size (after Russia and Canada) and by population (after China and India); Denali (Mt. McKinley) is the highest point (6,190 m) in North America and Death Valley the lowest point (-86 m) on the continent

note 2: the western coast of the United States and southern coast of Alaska lie along the Ring of Fire, a belt of active volcanoes and earthquake epicenters bordering the Pacific Ocean; up to 90% of the world's earthquakes and some 75% of the world's volcanoes occur within the Ring of Fire

note 3: the Aleutian Islands are a chain of volcanic islands that divide the Bering Sea (north) from the main Pacific Ocean (south); they extend about 1,800 km westward from the Alaskan Peninsula; the archipelago consists of 14 larger islands, 55 smaller islands, and hundreds of islets; there are 41 active volcanoes on the islands, which together form a large northern section of the Ring of Fire

note 4: Mammoth Cave, in west-central Kentucky, is the world's longest known cave system with more than 650 km (405 miles) of surveyed passageways, which is nearly twice as long as the second-longest cave system, the Sac Actun underwater cave in Mexico - the world's longest underwater cave system (see "Geography - note" under Mexico);

note 5: Kazumura Cave on the island of Hawaii is the world's longest and deepest lava tube cave; it has been surveyed at 66 km (41 mi) long and 1,102 m (3,614 ft) deep

note 6: Bracken Cave outside of San Antonio, Texas is the world's largest bat cave; it is the summer home to the largest colony of bats in the world; an estimated 20 million Mexican free-tailed bats roost in the cave from March to October making it the world's largest known concentration of mammals

note 7: the US is reliant on foreign imports for 100% of its needs for the following strategic resources - Arsenic, Cesium, Fluorspar, Gallium, Graphite, Indium, Manganese, Niobium, Rare Earths, Rubidium, Scandium, Tantalum, Yttrium; see Appendix H: Strategic Materials for further details

note 8: three food crops are generally acknowledged to be native to areas of what is now the United States: cranberries, pecans, and sunflowers

note 1: the country lies on major sea and air routes linking North and South America

note 2: Venezuela has some of the most unique geology in the world; tepuis are massive table-top mountains of the western Guiana Highlands that tend to be isolated and thus support unique endemic plant and animal species; their sheer cliffsides account for some of the most spectacular waterfalls in the world including Angel Falls, the world's highest (979 m) that drops off Auyan Tepui

note 1: the world is now thought to be about 4.55 billion years old, just about one-third of the 13.8-billion-year age estimated for the universe; the earliest widely accepted date for life appearing on earth is 3.48 billion years ago, but this date is conservative and may get pushed back further

note 2: although earthquakes can strike anywhere at any time, the vast majority occur in three large zones of the earth; the world's greatest earthquake belt, the Circum-Pacific Belt (popularly referred to as the Ring of Fire), is the zone of active volcanoes and earthquake epicenters bordering the Pacific Ocean; about 90% of the world's earthquakes (81% of the largest earthquakes) and some 75% of the world's volcanoes occur within the Ring of Fire; the belt extends northward from Chile, along the South American coast, through Central America, Mexico, the western US, southern Alaska and the Aleutian Islands, to Japan, the Philippines, Papua New Guinea, island groups in the southwestern Pacific, and New Zealand

the second prominent belt, the Alpide, extends from Java to Sumatra, northward along the mountains of Burma, then eastward through the Himalayas, the Mediterranean, and out into the Atlantic Ocean; it accounts for about 17% of the world's largest earthquakes; the third important belt follows the long Mid-Atlantic Ridge