Daniel Huffman has produced some interesting maps of the US’s major river systems, done in the style of intracity rail line maps. I especially like the one of the Columbia’s system.
He talks about generating these river maps here.
Naturally, he has other interesting things to say about maps, such as a discussion on projection conformality.

Accidentally compare a character and an integer.
$ python -c 'print "\0" > 1024'
True

Wait, what? Any character is larger than any integer? Why are chars and ints intercomparable then? Shouldn’t I get either a type error or a meaningful comparison? This seems like it’s guaranteed to be wrong!