This explains much and perhaps why liberals focus on tolerance, in a city with so many groups we have to find a way to get along, and in the countryside with more homogeneity the concerns are more about preserving the self-reliance they have come to value.
The American past was one where you could claim a piece of land and make your own home but it was also dangerous and you also had to defend it with help being miles or days away. This frontier mindset is a deep part of those rural value even if we no longer have a frontier.
Also in our history was the fact that many groups flocked to the cities, for jobs, and just as a general global trend. Minorities were among these groups (African-Americans leaving the South for industrial cities in the North and Mexican-Americans leaving the countryside for the larger cities in the Southwest) and thus why minorities consistently vote in blocs to represent urban values.
What other examples could you offer?
The voting data suggest that people don't make cities liberal -- cities make people liberal. Here, courtesy of Princeton's Robert Vanderbai, is an electoral map that captures the divisions:
The only major cities that voted Republican in the 2012 presidential election were Phoenix, Oklahoma City, Fort Worth, and Salt Lake City. With its dominant Mormon population, Mitt Romney was a lock in the Utah capital; Phoenix nearly voted for Obama. After that, the largest urban centers to tilt Republican included Wichita, Lincoln, Neb., and Boise.
The gap is so stark that some of America's bluest cities are located in its reddest states. Every one of Texas' major cities -- Austin, Dallas, Houston, and San Antonio -- voted Democratic in 2012, the second consecutive presidential election in which they've done so. Other red-state cities that tipped blue include Atlanta, Indianapolis, New Orleans, Birmingham, Tucson, Little Rock, and Charleston, S.C. -- ironically, the site of the first battle of the Civil War. In states like Nevada, the only blue districts are often also the only cities, like Reno and Las Vegas.
Awesome graphs and the rest of the article can be found here:
The poll also includes a suburban option because I strongly suspect that many in suburban areas tend to hold more rural values instead of urban ones.