Where I come from, it's pretty poor form to ask people to cite sources for obvious statements, without any other insight or commentary. After all, you're asking them to do work for you, but not taking basic steps to suggest you might appreciate their effort.
The preferred option is to do a little reading of your own beforehand, and to share whatever it is you know that makes you think the obvious answer might not be right.
>80% of the American population lived in what is called an urban area in the 2010 census [1]. While their definition of urban is looser than you might use, still >60% lived in 'cities'[2].
Unless the wealthier, more connected, more educated readership of Hacker News strongly bucks every trend suggested by their demographics, it's pretty safe to say we mostly live in urban areas.
The preferred option is to do a little reading of your own beforehand, and to share whatever it is you know that makes you think the obvious answer might not be right.