Photo of San Francisco by Todd LappinSilicon Valley is joined at the hip with San Francisco, and the hip is hugged by two major vein and artery lines: the 101 and the 280.

Every week, a new story appears that predicts the death of Silicon Valley. As entrepreneurs opt to start companies in hip, urban sprawls like San Francisco and New York, the argument is made that the technology hub has has lost its edge as the center of the entrepreneurial economy. Just this weekend, Silicon Valley was panned in the New York Times and the Wall Street Journal.

The argument is flawed if you consider that San Francisco and Silicon Valley are inter-connected. They are like conjoined twins that share the same heart.

Even our local paper has broadened its definition. The San Jose Mercury News recently argued that when we talk about Silicon Valley, we mean San Francisco too, which is by some measures the startup capital of the world. As the Merc’s columnist, Chris O’Brien, put it: “This is recognition, perhaps overdue, that the kinds of entrepreneurial companies and industries once tightly clustered in the South Bay can now be found throughout the region.”

For companies like Twitter, it’s merely a practical choice to be in the city. To encourage tech startups to set up shop in the seedier mid-market neighborhood in San Francisco, tax breaks were offered by the city’s board of supervisors. For younger startups, it’s a hiring tactic. “Young and talented developers and designers expect you to be in San Francisco,” said Cullen Wilson, chief executive of Sponsorfied, a Y Combinator-backed startup which recently re-located from Mountain View.

Most successful entrepreneurs have one foot in Silicon Valley, where most of the venture capital firms remain, and another in the city. Google has a huge office in San Francisco and a headquarters in Mountain View. Google, as well as Facebook, LinkedIn and others, operate free shuttle buses so their younger employees can enjoy a vibrant social life in the city. The top incubators and accelerator programs like Y Combinator still operate in Silicon Valley, but many of the young graduates flock to San Francisco.

The point is that in the Bay Area, it doesn’t make much of a difference whether a startup is based in the city or the ‘burbs. Silicon Valley is a physical place, sure. It lies between two mountain ranges, Mount Diablo and the Santa Cruz Mountains, but it’s also a culture. And culturally speaking, San Francisco is Silicon Valley — albeit with a few art museums, nightclubs and achingly hip coffee shops thrown into the mix. It shares the one-track or ‘one-tech’ mind. Just as it is in Silicon Valley, life in San Francisco is a whirlwind of happy hours, hackathons, and networking events.

New York’s answer to Silicon Valley (“Silicon Alley”) may dominate in certain sectors like e-commerce and media. But joined at the hip with San Francisco, the Bay Area remains the top pick for entrepreneurs.

Silicon Valley has fortified and expanded, and it won’t go down without a fight.

Photo credit: Todd Lappin/Flickr