North America, the third-largest continent, extends from the tiny Aleutian Islands in the northwest to the Isthmus of Panama in the south.

North America's physical geography, environment and resources, and human geography can be considered separately.

North America benefits greatly from its fertile soils, plentiful freshwater, oil and mineral deposits and forests. With a strong domestic and export economy focused on this abundant array of natural resources, North America has become one of the most developed regions in the world.

Agriculture

From the freezing Arctic to the tropical jungles of Central America, North America enjoys more climate variation than any other continent. Almost every type of ecosystem is represented somewhere on the continent, from coral reefs in the Caribbean to the ice sheet in Greenland. These differences contribute to North America's variety of agricultural industries, which are often divided by climate zone: tropical zone, subtropical zone, cool temperate zone and dry zone.

In the tropical zones of North America, farmers harvest oranges, sugar cane, coffee, cocoa and bananas. These crops grow on coastal plains and humid mountain slopes. Cotton and hemp are cultivated in the warmer and drier intermediate climate zone. These crops are important exports for Central American countries.

Fruits, vegetables, cotton and tobacco are predominant in the warm, subtropical zones of northern Mexico and the United States. Important agricultural areas in this zone include the Rio Grande Valley (citrus fruits) in the U.S. state of Texas and Mexico, California's Central Valley (fruits and vegetables), the Gulf Coastal Plain (vegetables), and the sandy valleys of the Appalachian Mountains (cotton and tobacco). These areas benefit from ample rain and warm air currents.

Agriculture in North America's tropical and subtropical zones is threatened by monoculture. Monoculture is the practice of growing one crop in an area over a long period of time. Monoculture is a risky way of farming for two reasons. First, the soil may lose its nutrients. The nitrogen and phosphates in the soil do not have time to accumulate if the field is not allowed to be fallow, or rest. Planting other, less-intensive crops can also help the soil recover its natural nutrients. The second reason monoculture puts crops at risk is the possibility of disease. A disease affecting a single species of plant could devastate an entire crop, and the community's livelihood. Planting a variety of crops minimizes the risk of disease.

Farmers and agribusinesses combat the threats of monoculture with the use of fertilizers and pesticides. Fertilizers replenish nutrients such as phosphates and nitrates to the soil. Pesticides target diseases brought by pests of a single plant. However, extensive use of fertilizers and pesticides can have a harmful impact on the environment. Runoff from agricultural fields can pollute rivers, lakes and the ocean.

The continent's cool temperate zones are ideal for hardy fruits, such as apples and peaches. Important agricultural areas in this climate include: the Finger Lakes region of New York in the U.S.; the Niagara Peninsula in the Canadian province of Ontario; the Columbia River basin in the U.S. state of Washington and the Canadian province of British Columbia; and the valleys of the Appalachian Mountains. These areas benefit from excellent drainage and predictable, established frosts.

The Dairy Belt, Corn Belt and Wheat Belt are three agricultural areas in the continent's cool temperate zones.

Dairy animals, including cows, goats and sheep, feed on the hay and hardy small grains that thrive in New England and the Great Lakes-St. Lawrence region along the Atlantic coast. This is the Dairy Belt.

The Corn Belt, located between the Ohio River and the lower Missouri River, receives ample water and strong summer sun, ideal for corn and soybeans.

West of the Corn Belt, the Wheat Belt stretches from the U.S. state of Kansas through the Canadian Prairie provinces of Alberta, Saskatchewan and Manitoba. This vast area of the Great Plains allows wheat to be cultivated in both winter and spring.

Dry zones, common in the southwestern U.S. and northern Mexico, are ideally suited for livestock ranching. Ranches with thousands of cattle are common in this region. Traditionally, livestock fed on locally grown fodder such as prairie grasses. However, irrigation for fruit and cotton farming has drained water supplies in the region. Native grasses cannot nourish the huge herds of livestock kept by ranchers. Cattle, sheep, hogs, and other livestock are less likely to graze than to eat corn-based feed. In fact, most of the corn grown in the Corn Belt is feeder corn used for livestock feed.

Forestry

Forestry is a major economic activity for much of North America. In the United States, the timber industry is strong in the Pacific Northwest, the Gulf states and South Atlantic coastal plains. In Canada, forestry is a major industry in the provinces of Quebec, Ontario and British Columbia.

Forestry is the management, cultivation and harvesting of trees and other vegetation in forests. In the Pacific Northwest, for instance, logging companies harvest cedar, fir and spruce trees. Lumber from these trees is exported around the world for construction. Some of the continents largest paper mills are found in these temperate rain forests. In addition to paper, paper mills produce cardboard and fiberboard.

Overharvesting of timber is a concern throughout North America. The reduction of forested land reduces biodiversity and threatens the longevity of the timber industry. The logging industry and local governments must work together to develop sustainable plans to harvest timber.

The Mexican government, for example, created the ProArbol (pro-tree) campaign with the objectives of conserving and restoring forests. The campaign pledges to plant more than 250 million trees in urban and rural Mexico. ProArbol also works to ensure that Mexican forests positively influence biodiversity and human health.

Mining

Extractive activities, such as mining and drilling, dominate the North American economy. Mining provides billions of dollars and millions of jobs throughout the continent. North America is a leading producer of coal, used in energy production; bauxite, used to create aluminum; iron and copper, both used in construction; and nickel, used to create steel, which North American companies export around the world. Gold and silver mines operate in the western part of the continent. Visitors to Crater of Diamonds State Park, a mine in the U.S. state of Arkansas, can search for their own diamonds.

Extractive activities have been a major part of the economies of North America for hundreds of years. For example, gold mining helped spur development in the U.S. states of California and Alaska in the 19th century.

Coal remains a primary industry for the U.S., and is often linked with states near the Appalachians. Coal is a type of sedimentary rock found deep underground, formed from the remains of ancient plants. When burned, coal is an excellent source of energy and is mostly used as fuel for electricity-generating power plants. Coal can be mined underground or in large, open pits.

Mining is a dangerous industry. Coal is combustible, meaning it catches fire and explodes easily. Coal dust is toxic when breathed for long periods of time. Mines are vulnerable to collapse. Mining accidents have led companies and governments to pursue regulations that ensure greater safety for miners. In 2006, for instance, a coal mine in Sago, West Virginia, exploded. Thirteen miners were trapped hundreds of meters below ground. Only one miner survived. The so-called Sago mine disaster prompted calls for greater communication and safety technology to be employed at mining sites throughout North America.

Coal mining can also have a negative impact on the environment. Mountaintop removal mining (MTR) has eliminated entire mountain ecosystems in the Appalachians. This type of mining also results in coal waste products being stored near public land. Improper storage of these waste products has damaged ecosystems and threatened human health. In 2008, a massive spill resulted in 1.1 billion gallons of coal slurry being released near Kingston, Tennessee. The spill damaged homes and entered into the Emory and Clinch Rivers, killing large fish populations and threatening water supplies.

Drilling

North America is home to vast deposits of oil and natural gas, which are drilled for energy and fuel. Oil and gas extraction are key elements of North Americas economy. The United States, Canada and Mexico are among the world's top oil producers.

The Athabasca tar sands, in the Canadian province of Alberta, are the world's largest reservoir of heavy crude oil. More than 20 national and international extraction projects are established in the Athabasca tar sands. The extraction and processing of crude oil, however, destroys the areas boreal forests and diverts an incredible volume of water from local rivers. The heavy crude oil from tar sands also emits 20 percent more carbon dioxide than emissions from light crude oil.

Oil and gas extraction is the dominant industry around the Gulf and Arctic regions of North America. Mexico leads other North American countries as one of the top oil exporters in the world, largely because of its reserves in and around the Gulf. (Although both the United States and Canada produce more oil than Mexico, they also consume far more. Both countries are mostly importers, not exporters, of oil and natural gas.)

Oil and natural gas, like coal, are nonrenewable resources. Global demand for fossil fuels has caused multinational corporations to drill in remote and dangerous regions. Scientists and engineers have developed more complex technology to search for deposits. Oil companies are forced to drill deeper and in more remote areas to extract these resources. The impact of these extractive activities is unknown.

However, the Deepwater Horizon oil spill in April 2010 has put into question the safety and sustainability of high-tech extractive industries. Deepwater Horizon was an offshore oil rig in the Gulf of Mexico, capable of drilling to depths of 9,100 meters (30,000 feet). The rig exploded, killing 11 workers and causing a massive oil spill that took months to control. The impact on the environment was felt in the U.S. from Texas to Florida.

The Built Environment

North America's high level of economic development has promoted the construction of megacities, engineering marvels and advanced infrastructure.

A megacity is usually defined as an urban area with at least 10 million people. Mexico City, Mexico; New York, New York; and Los Angeles, California, are North America's megacities.

With 21.2 million people, Mexico City is the largest metropolitan area in the Americas. Industrial growth caused a demographic boom during the last half-century, increasing the areas population from 3 million people in 1950 to its present numbers. As with many megacities, Mexico City is currently experiencing slower growth than in the past. The economy has shifted from manufacturing to the service industry, which includes tourism, education, banking and sales. More people are moving out of the city itself and into the suburbs.

Mexico City is built on a swampy series of islands in a valley surrounded by volcanoes. As the population boomed, the areas delicate geology led to problems with flooding, runoff, wastewater management, pollution and earthquakes.

Los Angeles, California, is one of the fastest-growing cities on the continent. L.A. is the second largest city in the United States, with 3.83 million people in 2008; the entire metropolitan area has more than 15 million people. The city is known as the Entertainment Capital of the World, with many motion picture, television, and music production studios established there. Los Angeles is also considered a majority-minority city, as its racial composition is less than 50 percent white. According to U.S. Census figures, Angelenos of Latino origin account for 48.4 percent of the population.

Toronto, Ontario, Canada, is also considered one of the most ethnically diverse cities in the world. More than 50 percent of its population was born outside of Canada. The city's diverse community, low crime rates, clean environment and high standard of living make it one of the world's most livable cities.

Engineering marvels have defined North America over the last century. The Panama Canal, completed in 1914, is one of the most important waterways in the world. Its 80-kilometer (50 mile) length connects the Atlantic and Pacific Oceans through the Isthmus of Panama, making ship voyages dramatically shorter. Ships travelling from the west coast to the east coast of the United States, for example, cut their voyage by 8,000 nautical miles because they are not required to round Cape Horn at the southern tip of South America.

The Hoover Dam, completed in 1936, is another of North America's engineering milestones. Located on the Colorado River on the border between the U.S. states of Arizona and Nevada, the Hoover Dam creates Lake Mead, one of the largest manmade lakes in the world. The dam is used for flood control, electric power, irrigation and water supplies.

While it has contributed greatly to the development of the southwestern U.S., the Hoover Dam has also negatively impacted the Colorado River, its tributaries, and surrounding ecosystems. Construction of the dam basically eliminated the Colorado Delta ecosystem, as almost no water reaches the river's mouth. Communities in the Mexican state of Baja California are also prevented from using the river's water supplies.

Cities and economic development have spurred North American engineers and architects to construct some of the world's most striking buildings. Completed in 1976, Toronto's CN Tower is the tallest freestanding structure in the Western Hemisphere, standing at 553 meters (1,815 feet). All major Canadian radio stations, as well as wireless service providers, use the CN Tower for transmission.

North America's advanced infrastructure has allowed populations, services, and industries to prosper across the continent. With the first underground line opened in 1904, the New York City subway system is one of the oldest and most extensive public transportation systems in the world. It now has more than 450 stations, more than 354 kilometers (220 miles) of track, and delivered more than 1.575 billion rides in 2009.

Other infrastructure systems transport goods. Mexico's state-owned petroleum company, Pemex, transports crude oil and natural gas through more than 453 pipelines spanning 4,667 kilometers (2,900 miles). Pemex is one of the largest companies in the world.