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SAN FRANCISCO, CA - FEBRUARY 13: The downtown skyline is viewed from Potrero Hill just after sunset on February 13, 2014, in San Francisco, California. San Francisco continues to be a major global tourist destination and has experienced a high-tech boom in recent years. (Photo by George Rose/Getty Images)

SAN FRANCISCO, CA - FEBRUARY 13:  The downtown skyline is viewed from Potrero Hill just after sunset on February 13, 2014, in San Francisco, California. San Francisco continues to be a major global tourist destination and has experienced a high-tech boom in recent years. (Photo by George Rose/Getty Images)