USA 2008 (September 06th) San Francisco, California

San Francisco (/ˌsæn frənˈsɪskoʊ/), officially the City and County of San Francisco, is the financial, cultural, and transportation center of the San Francisco Bay Area, a region of 7.15 million people which includes San Jose and Oakland. The only consolidated city-county in California, it encompasses a land area of about 46.9 square miles (121 km²) on the northern end of the San Francisco Peninsula, giving it a density of about 17,179 people per square mile (6,632 people per km²). It is the most densely settled large city (population greater than 200,000) in the state of California and the second-most densely populated large city in the United States after New York City. San Francisco is the fourth most populous city in California and the 13th most populous city in the United States, with a population of 805,235 as of the 2010 Census. The San Francisco-Oakland-Fremont metropolitan area has a population of 4,335,391.

The Golden Gate Bridge is a suspension bridge spanning the Golden Gate, the opening of the San Francisco Bay into the Pacific Ocean. As part of both U.S. Route 101 and California State Route 1, the structure links the city of San Francisco, on the northern tip of the San Francisco Peninsula, to Marin County. It is one of the most internationally recognized symbols of San Francisco, California, and of the United States. It has been declared one of the modern Wonders of the World by the American Society of Civil Engineers. The Frommers travel guide considers the Golden Gate Bridge "possibly the most beautiful, certainly the most photographed, bridge in the world".

The United States of America (also called the United States, the U.S., the USA, America, and the States) is a federal constitutional republic comprising fifty states and a federal district. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D.C., the capital district, lie between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the south. The state of Alaska is in the northwest of the continent, with Canada to the east and Russia to the west, across the Bering Strait. The state of Hawaii is an archipelago in the mid-Pacific. The country also possesses several territories in the Pacific and Caribbean.

At 3.79 million square miles (9.83 million km²) and with over 312 million people, the United States is the third or fourth largest country by total area, and the third largest by both land area and population. It is one of the world's most ethnically diverse and multicultural nations, the product of large-scale immigration from many countries. The U.S. economy is the world's largest national economy, with an estimated 2011 GDP of $15.1 trillion (22% of nominal global GDP and over 19% of global GDP at purchasing-power parity).

The Americas, or America, are lands in the Western hemisphere, also known as the New World.

In the English language, the Americas refers to the landmasses of North America and South America with their associated islands and regions, while America refers almost exclusively to the United States of America.

The Americas cover 8.3% of the Earth's total surface area (28.4% of its land area) and contain about 13.5% of the human population (about 900 million people).

The Golden Gate is the North American strait connecting San Francisco Bay to the Pacific Ocean. Since 1937 it has been spanned by the Golden Gate Bridge. Technically, the 'gate' is defined by the headlands of the San Francisco Peninsula and the Marin Peninsula, while the 'strait' is the water flowing in between.

During the last Ice Age, when sea level was several hundred feet lower, the waters of the glacier-fed Sacramento River and the San Joaquin River scoured a deep channel through the bedrock on their way to the ocean. The strait is well known today for its depth and powerful tidal currents from the Pacific Ocean. Many small whirlpools and eddies can form in its waters.

Before the arrival of Europeans in the 18th century, the area around the strait and the bay was inhabited by the Ohlone to the south and Coast Miwok people to the north. Descendants of both tribes remain in the area.

The Golden Gate is often shrouded in fog. During the summer, the heat in the California Central Valley causes the air there to rise. This can create strong winds which pull cool moist air in from over the ocean through the break in the hills caused by the Golden Gate, commonly causing a stream of dense fog to enter the bay. The strait was surprisingly elusive for early European explorers, presumably due to this persistent summer fog. The strait is not recorded in the voyages of Juan Rodriguez Cabrillo nor Francis Drake, both of whom may have explored the nearby coast in the 16th century in search of the fabled Northwest Passage. The strait is also unrecorded in observation by Spanish galleons returning from the Philippines that laid up in nearby Drakes Bay. These galleons rarely passed east of the Farallon Islands (27 miles west of the Golden Gate), fearing the possibility of rocks between the Islands and the mainland.