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United States is situated in the central southern part of North America almost entirely in the western hemisphere and a neighbor of Canada to the north and Mexico to the south. The state of Alaska is in the northwest of the continent with Canada to its east, and the state of Hawaii is in the mid-Pacific. The largest state is Alaska, the smallest - Rhode Island. On July 4, 1776, the Second Continental Congress, meeting in Philadelphia, declared the independence of "the United States of America" in the Declaration of Independence. July 4 is celebrated as the nation's birthday.
Geographically, the whole country is a federal constitutional republic made up of 50 states (48 continental states, plus Alaska and Hawaii the two newest states) and one federal district - Washington, D.C., the capital district. Apart from the political states of the USA, the country also has territories outside which are "insular areas". Some of these are U.S. Virgin Islands, American Samoa and Northern Mariana Islands. The Commonwealth of Puerto Rico, in the Caribbean, is a dependent of the USA but retains commonwealth status.
The United States is the world's largest national economy in nominal terms and second largest according to purchasing power parity (PPP), representing 22% of nominal global GDP and 17% of gross world product (GWP). The United States' GDP was estimated to be $17.914 trillion as of Q2 2015. The U.S. dollar is the currency most used in international transactions and is the world's foremost reserve currency. Several countries use it as their official currency, and in many others it is the de facto currency. Its seven largest trading partners are Canada, China, Mexico, Japan, Germany, South Korea, and the United Kingdom. The United States has been a leader in scientific research and technological innovation since the late 19th century. In 1876, Alexander Graham Bell was awarded the first U.S. patent for the telephone. Thomas Edison's laboratory developed the phonograph, the first long-lasting light bulb, and the first viable movie camera. Nikola Tesla pioneered the AC induction motor and high frequency power transmission used in radio. In the early 20th century, the automobile companies of Ransom E. Olds and Henry Ford popularized the assembly line. The Wright brothers, in 1903, made the first sustained and controlled heavier-than-air powered flight.
In Physiology or Medicine, Physics, chemistry, Economics, Literature, Peace, this island nation produced 357 Nobel laureates so far. Massachusetts Institute of Technology (MIT), Stanford University, Carnegie Mellon University, and Harvard University are one of the leading universities for Informatics in United States. Numerous informatics journals are published from United States with good reputation. Several leading Institution in the country including University of California, Berkeley, Princeton University, University of Washington, University of Texas at Austin, California Institute of Technology (Caltech), Columbia University and others are spearheading the informatics research.