Subway/Metro/Train maps are interesting to me for some reason.  I think it’s the colors and lines that make it into it’s own little piece of art with a purpose.  The first time you look at a map you’re completely confused, then it starts to make sense once you give it some time and then finally you can project a little confidence in understanding how it flows.  That probably sounds really exasperating.  Anyways, a cool travel trends book you can get on Amazon for about $15.