Are certain regions more Democratic and some more Republican?

Yes, Texas has more Republicans than California.

Both before and after the 2016 election, there's been a lot of discussion over how inconvenienced the Democratic party is by "clustering" and "geography". A party that is strongest in urban areas, the "argument" goes, will and/or should always have trouble winning a majority of the country's districts or electoral votes.

Sometimes this "argument" is illustrated with maps, like this one I made off of Mike Bostock's block showing the 2016 presidential winner by county