Geographic overview:
The surface of the earth is approximately 70.9% water and 29.1% land. The former portion is divided into large water bodies termed oceans. The World Factbook recognizes and describes five oceans, which are in decreasing order of size: the Pacific Ocean, Atlantic Ocean, Indian Ocean, Southern Ocean, and Arctic Ocean. The land portion is generally divided into several, large, discrete landmasses termed continents. Depending on the convention used, the number of continents can vary from five to seven. The most common classification recognizes seven, which are (from largest to smallest): Asia, Africa, North America, South America, Antarctica, Europe, and Australia. Asia and Europe are sometimes lumped together into a Eurasian continent resulting in six continents. Alternatively, North and South America are sometimes grouped as simply the Americas, resulting in a continent total of six (or five, if the Eurasia designation is used). North America is commonly understood to include the island of Greenland, the isles of the Caribbean, and to extend south all the way to the Isthmus of Panama. The easternmost extent of Europe is generally defined as being the Ural Mountains and the Ural River; on the southeast the Caspian Sea; and on the south the Caucasus Mountains, the Black Sea, and the Mediterranean. Portions of Azerbaijan, Georgia, Kazakhstan, Russia, and Turkey fall within both Europe and Asia, but in every instance the larger section is in Asia. These countries are considered part of both continents. Armenia and Cyprus, which lie completely in Western Asia, are geopolitically European countries. Asia usually incorporates all the islands of the Philippines, Malaysia, and Indonesia. The islands of the Pacific are often lumped with Australia into a "land mass" termed Oceania or Australasia. Africa's northeast extremity is frequently delimited at the Isthmus of Suez, but for geopolitical purposes, the Egyptian Sinai Peninsula is often included as part of Africa. Although the above groupings are the most common, different continental dispositions are recognized or taught in certain parts of the world, with some arrangements more heavily based on cultural spheres rather than physical geographic considerations.

Map references:
Physical Map of the World

Area:
total: 510.072 million sq km
[see also: Area - total country ranks ]
land: 148.94 million sq km
[see also: Area - land country ranks ]
water: 361.132 million sq km
[see also: Area - water country ranks ]
note: 70.9% of the world's surface is water, 29.1% is land

Area - comparative:
land area about 16 times the size of the US
top fifteen World Factbook entities ranked by size: Pacific Ocean 155.557 million sq km; Atlantic Ocean 76.762 million sq km; Indian Ocean 68.556 million sq km; Southern Ocean 20.327 million sq km; Russia 17,098,242 sq km; Arctic Ocean 14.056 million sq km; Antarctica 14 million sq km; Canada 9,984,670 sq km; United States 9,826,675 sq km; China 9,596,960 sq km; Brazil 8,515,770 sq km; Australia 7,741,220 sq km; European Union 4,324,782 sq km; India 3,287,263 sq km; Argentina 2,780,400 sq km
top ten largest water bodies: Pacific Ocean 155.557 million sq km; Atlantic Ocean 76.762 million sq km; Indian Ocean 68.556 million sq km; Southern Ocean 20.327 million sq km; Arctic Ocean 14.056 million sq km; Coral Sea 4,184,100 sq km; South China Sea 3,595,900 sq km; Caribbean Sea 2.834 million sq km; Bering Sea 2.52 million sq km; Mediterranean Sea 2.469 million sq km
top ten largest landmasses: Asia 44,568,500 sq km; Africa 30.065 million sq km; North America 24.473 million sq km; South America 17.819 million sq km; Antarctica 14 million sq km; Europe 9.948 million sq km; Australia 7,741,220 sq km; Greenland 2,166,086 sq km; New Guinea 785,753 sq km; Borneo 751,929 sq km
top ten largest islands: Greenland 2,166,086 sq km; New Guinea (Indonesia, Papua New Guinea) 785,753 sq km; Borneo (Brunei, Indonesia, Malaysia) 751,929 sq km; Madagascar 587,713 sq km; Baffin Island (Canada) 507,451 sq km; Sumatra (Indonesia) 472,784 sq km; Honshu (Japan) 227,963 sq km; Victoria Island (Canada) 217,291 sq km; Great Britain (United Kingdom) 209,331 sq km; Ellesmere Island (Canada) 196,236 sq km
ten smallest independent countries: Holy See (Vatican City) 0.44 sq km; Monaco 2 sq km; Nauru 21 sq km; Tuvalu 26 sq km; San Marino 61 sq km; Liechtenstein 160 sq km; Marshall Islands 181 sq km; Saint Kitts and Nevis 261 sq km; Maldives 298 sq km; Malta 316 sq km

Land boundaries:
the land boundaries in the world total 251,060 km (not counting shared boundaries twice); two nations, China and Russia, each border 14 other countries
note: 46 nations and other areas are landlocked, these include: Afghanistan, Andorra, Armenia, Austria, Azerbaijan, Belarus, Bhutan, Bolivia, Botswana, Burkina Faso, Burundi, Central African Republic, Chad, Czech Republic, Ethiopia, Holy See (Vatican City), Hungary, Kazakhstan, Kosovo, Kyrgyzstan, Laos, Lesotho, Liechtenstein, Luxembourg, Macedonia, Malawi, Mali, Moldova, Mongolia, Nepal, Niger, Paraguay, Rwanda, San Marino, Serbia, Slovakia, South Sudan, Swaziland, Switzerland, Tajikistan, Turkmenistan, Uganda, Uzbekistan, West Bank, Zambia, Zimbabwe; two of these, Liechtenstein and Uzbekistan, are doubly landlocked
[see also: Land boundaries country ranks ]

Coastline:
356,000 km
note: 95 nations and other entities are islands that border no other countries, they include: American Samoa, Anguilla, Antigua and Barbuda, Aruba, Ashmore and Cartier Islands, The Bahamas, Bahrain, Baker Island, Barbados, Bermuda, Bouvet Island, British Indian Ocean Territory, British Virgin Islands, Cabo Verde, Cayman Islands, Christmas Island, Clipperton Island, Cocos (Keeling) Islands, Comoros, Cook Islands, Coral Sea Islands, Cuba, Curacao, Cyprus, Dominica, Falkland Islands (Islas Malvinas), Faroe Islands, Fiji, French Polynesia, French Southern and Antarctic Lands, Greenland, Grenada, Guam, Guernsey, Heard Island and McDonald Islands, Howland Island, Iceland, Isle of Man, Jamaica, Jan Mayen, Japan, Jarvis Island, Jersey, Johnston Atoll, Kingman Reef, Kiribati, Madagascar, Maldives, Malta, Marshall Islands, Mauritius, Mayotte, Federated States of Micronesia, Midway Islands, Montserrat, Nauru, Navassa Island, New Caledonia, New Zealand, Niue, Norfolk Island, Northern Mariana Islands, Palau, Palmyra Atoll, Paracel Islands, Philippines, Pitcairn Islands, Puerto Rico, Saint Barthelemy, Saint Helena, Saint Kitts and Nevis, Saint Lucia, Saint Pierre and Miquelon, Saint Vincent and the Grenadines, Samoa, Sao Tome and Principe, Seychelles, Singapore, Sint Maarten, Solomon Islands, South Georgia and the South Sandwich Islands, Spratly Islands, Sri Lanka, Svalbard, Taiwan, Tokelau, Tonga, Trinidad and Tobago, Turks and Caicos Islands, Tuvalu, Vanuatu, Virgin Islands, Wake Island, Wallis and Futuna
[see also: Coastline country ranks ]

Maritime claims:
a variety of situations exist, but in general, most countries make the following claims measured from the mean low-tide baseline as described in the 1982 UN Convention on the Law of the Sea: territorial sea - 12 nm, contiguous zone - 24 nm, and exclusive economic zone - 200 nm; additional zones provide for exploitation of continental shelf resources and an exclusive fishing zone; boundary situations with neighboring states prevent many countries from extending their fishing or economic zones to a full 200 nm

Climate:
a wide equatorial band of hot and humid tropical climates, bordered north and south by subtropical temperate zones that separate two large areas of cold and dry polar climates

Terrain:
the greatest ocean depth is the Mariana Trench at 10,924 m in the Pacific Ocean

Elevation:
lowest point: Bentley Subglacial Trench (Antarctica) -2,555 m
note: in the oceanic realm, Challenger Deep in the Mariana Trench is the lowest point, lying -10,924 m below the surface of the Pacific Ocean
highest point: Mount Everest 8,850 m
top ten highest mountains (measured from sea level): Mount Everest (China-Nepal) 8,850 m; K2 (Pakistan) 8,611 m; Kanchenjunga (India-Nepal) 8,598 m; Lhotse (Nepal) 8,516 m; Makalu (China-Nepal) 8,463 m; Cho Oyu (China-Nepal) 8,201 m; Dhaulagiri (Nepal) 8,167 m; Manaslu (Nepal) 8,163 m; Nanga Parbat (Pakistan) 8,125 m; Anapurna (Nepal) 8,091 m
note: Mauna Kea (United States) is the world's tallest mountain as measured from base to summit; the peak of this volcanic colossus lies on the island of Hawaii, but its base begins more than 70 km offshore and at a depth of about 6,000 m; total height estimates range from 9,966 m to 10,203 m
highest point on each continent: Asia - Mount Everest (China-Nepal) 8,850 m; South America - Cerro Aconcagua (Argentina) 6,960 m; North America - Denali (Mount McKinley) (United States) 6,190 m; Africa - Kilimanjaro (Tanzania) 5,895 m; Europe - El'brus (Russia) 5,633 m; Antarctica - Vinson Massif 4,897 m; Australia - Mount Kosciuszko 2,229 m

Natural resources:
the rapid depletion of nonrenewable mineral resources, the depletion of forest areas and wetlands, the extinction of animal and plant species, and the deterioration in air and water quality (especially in some countries of Eastern Europe, the former USSR, and China) pose serious long-term problems that governments and peoples are only beginning to address

Irrigated land:
3,096,621.45 sq km (2011 est.)
[see also: Irrigated land country ranks ]

Total renewable water resources:
53,789.29 cu km (2011)
[see also: Total renewable water resources country ranks ]

Natural hazards:
large areas subject to severe weather (tropical cyclones); natural disasters (earthquakes, landslides, tsunamis, volcanic eruptions)
volcanism: volcanism is a fundamental driver and consequence of plate tectonics, the physical process reshaping the Earth's lithosphere; the world is home to more than 1,500 potentially active volcanoes, with over 500 of these having erupted in historical times; an estimated 500 million people live near these volcanoes; associated dangers include lava flows, lahars (mudflows), pyroclastic flows, ash clouds, ash fall, ballistic projectiles, gas emissions, landslides, earthquakes, and tsunamis; in the 1990s, the International Association of Volcanology and Chemistry of the Earth's Interior, created a list of 16 Decade Volcanoes worthy of special study because of their great potential for destruction: Avachinsky-Koryaksky (Russia), Colima (Mexico), Etna (Italy), Galeras (Colombia), Mauna Loa (United States), Merapi (Indonesia), Nyiragongo (Democratic Republic of the Congo), Rainier (United States), Sakurajima (Japan), Santa Maria (Guatemala), Santorini (Greece), Taal (Philippines), Teide (Spain), Ulawun (Papua New Guinea), Unzen (Japan), Vesuvius (Italy)

Environment - current issues:
large areas subject to overpopulation, industrial disasters, pollution (air, water, acid rain, toxic substances), loss of vegetation (overgrazing, deforestation, desertification), loss of wildlife, soil degradation, soil depletion, erosion; global warming becoming a greater concern

Geography - note:
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