With the filibuster and U.S. Senate dysfunction now a front-burner issue, it's worth a look at what the Senate might look like if it were apportioned by population the way the House is.
Without the benchmarks of traditional state lines I can't tell if Iowa City ends up with Lincoln or with High Plains.
Of course, this scenario has one serious barrier: the one remaining un-amendable section of the Constitution states that no state can lose its equal Senate representation without its consent. (The other un-amendable section related to the slave trade.) I have my own idea for Senate reform; someday I might write it.
Here's some lists: