I think the numbers and statistics are flexible. In my case, I grew up in a tiny rural town of 2,500 and the county was considered underserved. I would disagree with the underserved, but there it is - according to amcas' rankings.
I have lived in large cities as an adult (7,000,000) adn now applying to UVM, I said I want to do rural medicine and they ask specifically for all places you've lived and the populations.
Even tho I have lived in big cities, I come from a rural community and so like post-ers have said above, I feel I would happily stay in a small rural community and my essays have all backed this up.
In the end, you could also come from Los Angeles and say you want rural med and as long as you can support that statement consistently, it shouldn't be too much of a problem.