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Philadelphia, often called Philly, is the largest city in the Commonwealth of Pennsylvania, the sixth-largest city in the U.S., and the second-largest city in both the Northeast megalopolis and Mid-Atlantic regions after New York City. Since 1854, the city has been coextensive with Philadelphia County, the most populous county in Pennsylvania and urban core of the Delaware Valley, the nation's seventh-largest and one of world's largest metropolitan regions with 6.245 million residents in 2020. The city's population at the 2020 census was 1,603,797, and over 56 million people live within 250 mi (400 km) of Philadelphia.

Philadelphia was founded in 1682 by William Penn, an English Quaker. The city served as capital of the Pennsylvania Colony during the British colonial era and went on to play a historic and vital role as the central meeting place for the nation's founding fathers whose plans and actions in Philadelphia ultimately inspired the American Revolution and the nation's independence. Philadelphia hosted the First Continental Congress in 1774 following the Boston Tea Party, preserved the Liberty Bell, and hosted the Second Continental Congress during which the founders signed the Declaration of Independence, which historian Joseph Ellis has described as "the most potent and consequential words in American history". Once the Revolutionary War commenced, both the Battle of Germantown and the Siege of Fort Mifflin were fought within Philadelphia's city limits. The U.S. Constitution was later ratified in Philadelphia at the Philadelphia Convention of 1787. Philadelphia remained the nation's largest city until 1790, when it was surpassed by New York City, and served as the nation's first capital from May 10, 1775, until December 12, 1776, and on four subsequent occasions during and following the American Revolution, including from 1790 to 1800 while the new national capital of Washington, D.C., was under construction.

With 18 four-year universities and colleges, Philadelphia is one of the nation's leading centers for higher education and academic research. As of 2021[update], the Philadelphia metropolitan area was the state's largest and nation's ninth-largest metropolitan economy with a gross metropolitan product (GMP) of US$479 billion. The city is home to five Fortune 500 corporate headquarters as of 2022. The Philadelphia skyline, which includes several globally renowned commercial skyscrapers, is expanding, primarily with new residential high-rise condominiums. Philadelphia and the Delaware Valley are a biotechnology and venture capital hub; and the Philadelphia Stock Exchange, owned by NASDAQ, is the nation's oldest stock exchange and a global leader in options trading. 30th Street Station, the city's primary rail station, is the third-busiest Amtrak hub in the nation, and the city's multimodal transport and logistics infrastructure, including Philadelphia International Airport, the PhilaPort seaport, freight rail infrastructure, roadway traffic capacity, and warehouse storage space, are all expanding.

Haidian District, which belongs to Beijing, is located in the west and northwest of Beijing, adjacent to Xicheng District and Chaoyang District in the east, Fengtai District in the south, Shijingshan District and Mentougou District in the west, and Changping District in the north. It covers an area of 431 square kilometers, with a boundary line of about 146.2 kilometers, 30 kilometers from north to south, and 29 kilometers from east to west, accounting for about 2.6 percent of the total area of Beijing. The area is between 39 °53 degrees north latitude and 40 degrees 09 degrees north latitude and 116 degrees 23 'east longitude. In the early Yuan Dynasty, the town of Haidian was near a shallow lake, so it was called "Haidian", that is, Haidian today. In September 1952, Haidian District was officially named, and the area under its jurisdiction was formed in January 1963. As of 2018, Haidian District has jurisdiction over 22 streets and 7 districts. As of
Airport In Haidian - Beijing Capital International Airport
Beijing Capital International Airport (Beijing Capital International Airport, IATA: PEK, ICAO: ZBAA), located in the northeast suburb of Beijing, China, 25 kilometers southwest of Beijing city center, 67 kilometers south of Beijing Daxing International Airport, is a 4F international airport   , is one of the three major portal complex hubs in China   , members of the international air cargo hub group in the Bohai Rim region   , the world's largest airport   .
Beijing Capital International Airport was built in 1958. On January 1, 1980, supporting projects such as the T1 terminal building, the apron, and the parking lot in front of the building were completed and officially put into use. On November 1, 1999, the T2 terminal was officially put into use, and at the same time, the T1 terminal was closed for renovation. On September 20, 2004, the T1 terminal was put into use again. In the spring of 2008, the airport expansion project (Terminal T3) was completed.  
As of July 2017, Beijing Capital International Airport has three terminal buildings with a total area of ​​1.41 million square meters; there are two 4F runways and one 4E runway   The length and width are 3800×60 meters, 3200×50 meters, 3800 meters×60 meters respectively; there are 314 seats in total; 252 domestic and foreign routes have been opened.    
From 1978 to 2018, the annual passenger throughput of Beijing Capital International Airport increased from 1.03 million to 101 million, ranking first in Asia and second in the world.   In 2019, the passenger throughput of Beijing Capital International Airport was 100.013 million passengers, a year-on-year decrease of 1.0%; the cargo and mail throughput was 1.9553 million tons, a year-on-year decrease of 5.7%; , No. 2, No. 1.  
In 2021, Capital Airport will add three new domestic destinations, namely Huai'an, Tumusuk and Jingzhou   .
Travel Sights In Haidian
Travel Notes In Haidian
Travel Asks In Haidian
Travel Asks In Haidian