Pew Research data on how many countries people have travelled to
25
votes
2017 edition (Interactive version)
It's really interesting and pretty useful to know how the 2 US parties are split and which voting blocks have dissappeared and emerged over time and some blocks don't really fit all too well in the 2 parties (most notably the religious left). This also serves as a kind of model for what a multiparty US might look like.