In terms of gerrymandering and vote packing. Does the denser population in the Democratic cities help the Republicans, who are more spread out among the metro fringe and the rural areas?
Yes, but the problem isn't population density as much as the fact that you might have a city that votes 70% Democratic surrounded by suburbs that vote 55% Republican. With a map that doesn't visually look gerrymandered, the city is a Democratic vote sink while Republicans win the suburbs. A fair map should look a little gerrymandered for the Democrats. A map that is drawn heavily in favor of Democrats, like this one, ends up looking epic.
http://www.swingstateproject.com/diary/6166/
