It is a known fact that large cities tend to support the Democratic Party. There are many reasons for this. Primarily, democratic majorities living in big cities like welfare recipients, unions, highly educated citizens and white collar workers, tend no to worry about things like the cost to produce the food they eat or the energy they use.
These metro-citizens living in their city cocoons are completely shelter from how difficult it is to produce the food they eat, or how costly it can be to produce the energy they utilized. Most of them tend to take for granted all these benefits they enjoy. Obviously, is not a problem for them to support legislation to increase taxes for energy companies.
On the other hand, people living in vast country areas do not have all the amenities that city dwellers enjoy, so they tend to vote Republican.
Furthermore, urban populations and well educated people are mostly open-minded so they support things like gay marriage and abortion, which are main issues for Democrats. Now, many people living in rural areas could also have the same view of the people living in big cities, but social science tell us that when we compare, most of urban people have these views.
