There are 14 countries and 2 regions in Oceania. The details are shown in the table below:
||Population (ten thousand)
||Federated States of Micronesia
||Papua New Guinea
||Papua New Guinea
Note: The territory of the Republic of Indonesia spans Asia and Oceania. ,
Oceania, with a total land area of about 8.97 million square kilometers, accounts for about 6% of the world's total land area, and is the smallest continent in the world. Except for Antarctica, it is the world's least populous continent. It is located in the central and southern equatorial oceans of the Pacific Ocean. Between Asia and Antarctica, it borders the Indian Ocean to the west and the Pacific Ocean to the east, and is far away from North and South America.
The English name of Oceania is Oceania, which means "land surrounded by the ocean", where "Ocean" means "the sea" and the suffix -ia means land. This name appeared in 1812 and was coined by the Danish geographer Malte-Brun. The English "Australia" (Australia) can sometimes be used as a continent name, but it refers to a smaller range than Oceania, excluding Melanesia, Micronesia and Polynesia.
Oceania straddles the northern and southern hemispheres, from 47° south latitude to 30° north latitude, and across the east and west hemispheres, from 110° east to 160° west. The distance between east and west is more than 10,000 kilometers, and the distance between north and south is more than 8,000 kilometers. The countless islands scattered in the vast ocean include Australia, New Zealand, New Guinea (Ilian Island) and the three major island groups of Melanesia, Micronesia, and Polynesia. There are 14 independent countries in Oceania, and the remaining 10 regions are still under the jurisdiction of the United States, Britain, France and other countries. There are significant differences in the level of economic development among countries. Australia and New Zealand are developed countries, and other island countries are mostly agricultural countries with relatively backward economies. Industry is also mainly concentrated in Australia, followed by New Zealand. It is geographically divided into six regions: Australia, Papua New Guinea, New Zealand, Melanesia, Micronesia and Polynesia.
Oceania has a total of about 29 million people, making it the least populous continent in the world except Antarctica. It accounts for about 0.5% of the world's population. 65% of the continent's population is located in mainland Australia. There are significant differences in population density among island countries. Local residents such as Papuans, Australians, Tasmanians, Maori, Melanesians, Micronesians and Polynesians account for about 20% of the total population, and European descent account for more than 70% , In addition to mixed races, Indians, Chinese and Japanese. The aboriginal inhabitants are yellow people (Polynesians, etc.) and brown people (Australian aborigines).
Oceania has a small land area, but there are many islands scattered on the vast Pacific Ocean. The latitudes spanned between the north and the south have obvious differences in climate and various types.
The western part of Oceania is the birthplace of tropical cyclones. There are two central areas in which they occur. One is attached to the Caroline Islands and attacks the southeastern coast of Asia; the other occurs near Samoa, Tonga and Fiji and invades northeastern Australia.
1. Wide range of tropical and subtropical: Although the continents and islands of Oceania are widely distributed, most of them are between 30° north and south latitudes. Most areas belong to the tropical and subtropical areas: although most areas are under the sun's vertical irradiation, Because the vast ocean is not too hot, most of the annual average temperature is between 25°C and 28°C. The continental part of Oceania and the archipelago in the tropical and subtropical range are very different in area, latitude and distance from the sea, combined with the topography and atmospheric circulation, so the temperature difference between the Australian continent and the archipelago is obvious. Because of the small area of the islands, the archipelago can fully adjust the climate of the ocean. Although it has a tropical and subtropical climate, the temperature is not too high and the ocean is obvious. The annual average temperature of the islands in Oceania is between 26°C and 28°C. Except for some islands, the annual average temperature rarely exceeds 29°C or below 24°C.
2. Arid regions account for a large proportion of the land area: Oceania's annual rainfall is less than 250 mm, accounting for 30% of the total area, the annual rainfall of 250 mm, 500 mm of the area accounted for 28%, the two together accounted for 58% of the total area. More than half of the land area of Oceania is arid area. Compared with other continents, the arid regions of Oceania account for the continent's land area, surpassing Asia and Africa. The average annual rainfall in Oceania is about 700 millimeters, which is only similar to that of Africa, which is less rainy, and is less than 1/5 of the average rainfall in all continents.
3. Significant differences in the regional distribution of precipitation: From the perspective of precipitation distribution, the precipitation in parts of the eastern archipelago of Oceania is much greater than that in the western continental area, and it has the characteristics of decreasing from east to west and from the equator to the north and south. The central and western parts of the Australian continent have a dry climate with an annual rainfall of less than 250 mm, and the annual rainfall near Lake Eyre is less than 120 mm. It is the region with the least precipitation in the continent; and the northeastern part of Kauai Island in the Hawaiian Islands has an average annual rainfall of up to 12,000 mm, which is one of the regions with the highest rainfall in the world.
4. The tropical climate types are diverse: the equator passes through the north of the central part of the continent, and the land area between the Tropic of Cancer accounts for about 60% of the total area of the continent. The tropical area is comparable to Africa and South America. In the tropics, there are both large continents and numerous islands surrounded by the ocean; both the vast inland under the control of the return high pressure and the island groups deeply affected by the trade winds; both are located near the equator with high temperatures Rainy areas, but also dry and wet seasons affected by summer monsoons. Oceania has 8 climate types, of which 4 are tropical types. The distribution of climate types outside the tropics is not large.
Climate type area
1. Tropical marine climate zone: It is the climate type zone with the widest distribution in this continent. Such as the New Hebrides, Fiji Islands, Santa Cruz Islands in the Melanesian Islands; Hawaiian Islands, Tonga Islands, Samoa, Society Islands, Tuamotu Islands, etc. in the Polynesian Islands; The Marshall Islands, the Caroline Islands, and the Mariana Islands in the Micronesian Islands all have a tropical marine climate. It is surrounded by tropical oceans, with the influence of warm currents and the adjustment of sea breeze, so the climate is warm and rainy. The annual average temperature is between 23-26℃.
2. Tropical rain forest climate zone: mainly distributed near the equator, such as the northwest and north of Irian Island (New Guinea), New Britain, Bismarck Islands, parts of the Solomon Islands, and Gilbert Islands, etc., all belong to tropical rain forests climate. It is hot and rainy throughout the year, with small inter-annual variations in temperature. The annual average temperature is about 27°C, and the annual difference is 1°C~3°C. The precipitation is bimodal, with an annual precipitation of 2000-3000 mm. Due to the influence of topography, the precipitation can reach 5000- 6000 mm.
3. Tropical wet and dry season climate zone: Mainly distributed in the Kimberley Plateau, Arnhem Land, Cape York Peninsula on the Australian continent, the coast north of 25° south latitude in the east of the mainland; and the southern plain of Irian Island. The dry and wet seasons here are distinct. The summer (January) is affected by the tropical ocean air mass brought by the northwest monsoon, so it is hot and humid with abundant rainfall; the winter (July) is affected by the southeast trade wind from the continental high pressure and is dry. , Become the dry season. The temperature in this area is relatively high throughout the year, and the annual average tears are generally above 25°C. The annual rainfall is abundant, and the rainfall and the length of the rainy season vary depending on the geographical conditions of each region. 
4. Tropical arid and semi-arid climate zone: This zone is the most extensive climate zone in Oceania: distributed in the central and western parts of the Australian continent, where the climate is arid and deserts are widespread. The annual average temperature is 18-25℃; the summer is hot, the average temperature in January is 21-30℃; the winter is mild, the average temperature in July is 13~17℃; the precipitation is scarce, the evaporation is strong, and the annual precipitation in inland areas is less than 200 Millimeter is a desert area on the mainland, from inland to north or south, the annual precipitation is 250 to 500 millimeters, which is a semi-desert area.
5. Subtropical humid climate zone: Distributed in the coastal areas of New South Wales and southeastern Victoria in the Australian mainland, as well as the northern part of the North Island of New Zealand, where the climate is mild and humid. The average temperature of the hottest month (January) is generally 18-20℃, and the coldest month (July) is above 8℃. The annual precipitation is 700 to 1500 mm, and the precipitation is evenly distributed during the season. In summer, easterly winds from the ocean often form topographical rain when it blows higher. In winter, there are more westerly winds, which are cyclonic rains. The distribution of precipitation decreases from the coast to the inland.
6. Subtropical continental arid and semi-arid climate zone: Located inland in the southeastern part of the Australian continent, between the subtropical humid climate zone and the tropical arid and semi-arid climate zone. The annual precipitation gradually decreases from about 500 mm in the east to the west, to below 250 mm. The temperature is above 25℃ in summer, mild in winter, and above 9℃ in the coldest month.
7. Subtropical summer and dry climate zone: Located in the southwest corner of the Australian mainland, and the area centered on Adelaide. Under the control of the Indian Ocean high pressure in summer, it is hot and dry. In winter, it is affected by the northward westerly wind. Cyclone activity is frequent and mild and humid. The hottest month in summer (January or February) has an average temperature of 18-24°C, and the coldest month in winter is July above 12°C. The annual precipitation is about 500-1000 mm, and summer precipitation only accounts for 4%-9% of the annual precipitation. The precipitation decreases from west to east and from south to north.
8. Temperate maritime climate zone: including New Zealand's South Island and South North Island, Tasmania, etc. Under the control of warm and humid westerly winds throughout the year, there is neither scorching heat nor severe winter. The average annual temperature is 10~15℃. The average temperature in January varies from north to south at 19.14℃. The average temperature in July is 11℃ in the north and 5℃ in the south. The annual difference is relatively small. The precipitation is abundant throughout the year, with frontal precipitation dominated. It is the only area in Oceania where snow falls in winter.
Oceania rivers appear to be very scarce. The rivers are short and have little water volume. The water volume in the rainy season is soaring, and the flow is sometimes cut off in the dry season, and most of them are not conducive to navigation. The main rivers are Australia’s Murray River and its tributaries Darling River and Malambiji River, Roper River, Gilbert River, Flinders River, New Zealand’s Clutha River, Waikato River and New Guinea’s Sepi Ke River, Fry River, Mambo Lamo River, etc.
There are about 146 lakes in the world with an area of more than 1,000 square kilometers, of which 4 are in Oceania. The total amount of fresh water resources is 2390km³, which is 267,000 cubic meters per square kilometer. Compared with other continents, Oceania has fewer lakes, and most of the lakes on the continent are saltwater lakes. There are 186 lakes at an altitude of 20m or more and more than 54% of the lakes are located in Australia. The number of lakes in New Zealand is 43, accounting for 23.1% of the total number of lakes, followed by Papua New Guinea, which has nearly 21% of the lakes.
The largest lake in Oceania is Lake Eyre (Lake Eyre) in Australia. It has the largest area (when it is full) of 9,500 square kilometers. It is divided into Lake Eyre and Lake Eyre. The two lakes are narrow. The Goyd Waterway, its water volume changes with precipitation; the deepest lake in Oceania, Lake Manapouri in the southwestern mountains of New Zealand's South Island, is 443 meters deep.
Oceania straddles the three major plates of the Indo-Australia plate, the Pacific plate and the Eurasian plate. The region has experienced a long history of tectonic evolution from the Archean to the present. According to regional geological characteristics, the area can be divided into 3 primary structural units, namely the Precambrian craton in central and western Australia, the Paleozoic orogenic belt in eastern Australia, and the Mesozoic and Cenozoic island arc of the Pacific Rim, 12 secondary structural units and 40 three-level structural units.
The geological structural characteristics of Oceania are mainly manifested in the relatively stable crust of the ancient continents, the frequent tectonic activities of the islands formed in the new period, and the development of terranes from west to east from old to new.
Oceania is made up of the world's smallest Australian continent and more than 10,000 islands with huge differences in area. The number of islands is the highest among all continents. The area of islands accounts for 13.8% of the total area of the continent, and its proportion is second only to North America, ranking second in the world. Oceania not only has many islands, but also a wide range of types. According to its genesis, it can be divided into four types: continental type, volcanic type, coral type and mixed type. If combined with the subdivision of the appearance, the volcanic type can be divided into Hawaiian and Vesuvius, and the coral type can be divided into three types: platform reef, atoll and skirt (barrier) reef.
In Oceania, the altitude is generally below 600 meters, except for some mountainous areas that exceed 2000 meters above sea level. The plains below 200 meters above sea level account for about 1/3 of the continent's area, and the hills and terraces between 200 and 600 meters account for more than 1/2 of the continent's area. It is a low-lying continent in the world. The central and western parts of the Australian continent are vast, with arid climate, sparse vegetation, strong wind, and extensive wind erosion and aeolian landforms on the surface. In the western desert and the central Eyre Lake area, there are many sand dunes, sand ridges and saucers formed by wind deposition. Wind-eroded sandstone pillars and typical Yadan topography can be seen near the MacDonnell Ranges.
The formation of islands in Oceania is mostly related to volcanism. The bases of coral islands and atolls are also composed of volcanic materials, so volcanic landforms are widely distributed and diverse in forms. For example, New Zealand has clusters of volcanic craters and lava bends: Hawaii and Polynesia have large and small-slope shield-shaped volcanic landforms.
The geomorphic structure of Oceania has five distinct geomorphic units from west to east: the erosion plateau in the western part of the mainland (the Western Australia plateau), the subsidence plain in the central part of the mainland (the China-Australia Plain), and the fault-block mountain in the eastern part of the mainland (the Dongao Mountains), The new fold island arc (continental island) on the east side of the mainland, and the volcanic-coral island group (oceanic island) further east.