I think this has more to do with you and the local culture (like, block-by-block) than urban vs. suburban. in the suburbs, you can drive back and forth between

I think this has more to do with you and the local culture (like, block-by-block) than urban vs. suburban. in the suburbs, you can drive back and forth between your home garage and office and never speak to anyone. but you can do the same thing on foot in a city. in my city, people don't usually strike up conversations with random strangers on the street. or if they do, it's just a one-off; you'll probably never see that person again. in the suburbs, if you spend a lot of time on your porch, you'll probably get to know the neighbors that hang out on their porches. there's a pretty similar dynamic on the stoops of residential blocks in a city. if I had to make a general rule, I'd say there are more people who could potentially be your friend in a city, but the barrier to becoming friends with each one is higher. you bump in to more people, but less frequently.