The most popular two-letter combos in English

I was pondering how one would make a premium gibberish generator the other day, which led to a short investigation of which pairings of letters are legal in English and how common each combination is. This diagram shows a basic heat map of letter combinations, using '^' to mark the beginning of a word and '$' to mark the end. The data here is extracted from every item in the "2 of 12" list of dictionary words available on Kevin's Word List page.

Click a square to see instances of the combination (up to 150 examples).

Note that this is different from the frequency with which two-letter combos ("digraphs") occur in the wild. When the frequency of each word in the corpus is considered, "th" usually comes out on top.