overall share trading value and by total market capitalization of their listed companies in 2013. The NYSE American (formerly the American Stock Exchange, AMEX), New York Board of Trade, and the New York Mercantile Exchange (NYMEX) are also located downtown. Financial technology (fintech) and cryptocurrency have emerged as more recent constituents of the financial sector as well as the tech sector. Corporate sector New York City is home to the most corporate headquarters of any city in the United States, the overwhelming majority based in Manhattan. Manhattan contained over 500 million square feet (46.5 million m2) of office space in 2018, making it the largest office market in the United States, while Midtown Manhattan, with 400 million square feet (37.2 million m2) in 2018, is the largest central business district in the world. New York City's role as the top global center for the advertising industry is metonymously reflected as "Madison Avenue". Tech and biotech Silicon Alley, centered in Manhattan, has evolved into a metonym for the sphere encompassing the New York City metropolitan region's high tech industries, including the Internet, new media, telecommunications, digital media, software development, biotechnology, game design, financial technology (fintech) and cryptocurrency blockchain technology, and other fields within information technology that are supported by the area's entrepreneurship ecosystem and venture capital investments. , New York City hosted 300,000 employees in the tech sector. In 2015, Silicon Alley generated over US$7.3 billion in venture capital investment, most based in Manhattan, as well as in Brooklyn, Queens, and elsewhere in the region. High technology startup companies and employment are growing in Manhattan and across New York City, bolstered by the city's emergence as a global node of creativity and entrepreneurship, social tolerance, and environmental sustainability, as well as New York's position as the leading Internet hub and telecommunications center in North America, including its vicinity to several transatlantic fiber optic trunk lines, the city's intellectual capital, and its extensive outdoor wireless connectivity. Verizon Communications, headquartered at 140 West Street in Lower Manhattan, was at the final stages in 2014 of completing a US$3 billion fiberoptic telecommunications upgrade throughout New York City. As of October 2014, New York City hosted 300,000 employees in the tech sector, with a significant proportion in Manhattan. The technology sector has been expanding across Manhattan since 2010. The biotechnology sector is also growing in Manhattan based upon the city's strength in academic scientific research