...Each comes in 3 versions: with country codes as specified in ISO-2 (two-letter codes), ISO-3 (three-letter codes), and full country names from no particular standard. In distance matrices (files with matrix in the filename), the first column represents a passport (=from), each remaining column represents a destination (=to). Files in tidy format (with tidy in filename) have three columns: passport (from), destination (to), and the requirement.