I had the same feeling when I lived in Porto and later visited San Francisco. The two cities have so much in common: similar temperatures, they're both famous for their bridges (Porto actually has several), the fog that rolls in regularly, and even their most iconic bodies of water both have "gold" in the name: the Golden Gate and Rio Douro (which means "golden river"). I think this comes from how the water looks golden at sunset, since both coastlines face west. And of course, both cities are known for their cable cars.