In his first column as Kickshaws editor in February 1989, Dave Morice showed how one could construct chains of state names using their postal codes: for example, MaINe contains the bigram IN which stand for Indiana, INDiana contains the bigram ND which stands for North Dakota. Recently, I realized that this is an example of a directed graph which I discussed in another context in " Directed Word Chains (part 1)" in the August 1991 Word Ways.
Eckler, A. Ross
"The Postal Union,"
Word Ways: Vol. 32
, Article 7.
Available at: https://digitalcommons.butler.edu/wordways/vol32/iss4/7