Silicon Valley is ground zero for the digital revolution. That makes San Francisco the best example of the saying, "The future is already here; it's just not evenly distributed."
Walk around the city and you'll likely cross paths with electric cars and wheeled robots making deliveries on sidewalks. You also may see self-driving car startups such as GM's Cruise testing vehicles across the city.
The area wasn't always a technology hotbed. U.S. Defense Department spending helped the Bay Area emerge as a technology hub in the 20th century. Hewlett-Packard, for example, was a defense contractor during World War II.
Now, San Francisco is perhaps the most obvious destination for a budding entrepreneur.
