I lived in a building smack in the middle of San Francisco and didn't know my neighbors either. The only real difference in a city is that your neighbors are 10 feet instead of 100 feet from you.
Maybe it is the neighborhood you were in, or that you don't make an effort to aproach people?
I live in San Francisco, and I know at least two of my neighbors. We are not friends or anything, but a hi and a small talk once and a while doesn't hurt. Unfortunately, i live in a building where people stay for few years, and move somewhere else, so I guess that doesn't help.
I also sub-leased an apt. in North Beach, for my visiting parents. The girl I subleased from, had lived in that apt. for about 10 years, and she knew most of her neighbors. She gave me three numbers, of neighbors that could help me, if something happened, and my parents were talking to her downstairs neighbors everyday.
Very nice people.
I also picked the key from one of her neighbors, so she trusted them.
Living in a place where people are less transient helps a lot.
From now and on, I am going to try to be more friendly to people I don't know. I have seen the opposite, where people are unfriendly, and I don't like it.
