There is always the question about the sequence. My own idea is: the Yi is an ancient moon-almanac, starting at new moon, and giving the meaning for every day of two consecutive moon-months. The first one yang, the second one yin, like the Chinese astrological signs. In the course of a sun-year, there are 6 of those double months, each with its own 'color'.
Several astrologers found images for every day of the year, some by clearsightedness, others by observing people in connection with their day of birth.
An interesting set of images are the Sabian Symbols.
There are four hexagrams with an absolute value, 1, 2, 63 and 64, they correspond with old yang, old yin, young yang and young yin. This leaves us with 60 hexagrams, in total 360 lines, one for every degree of the zodiac.