There are 64 hexagrams in all. They are created from all the possible pair combinations of 8 unique trigrams. Hexagrams are created by combining two trigrams. The relative position and the attributes of the trigrams are what give the hexagrams meaning. The lower trigram is said to be the inner trigram and is also considered to be below, within, behind and coming. The upper trigram is the outer trigram and is also considered to be above, without, in front and leaving.
In a hexagram, the first, third and fifth lines are considered to be superior strong positions representing the light. The second, fourth and sixth lines are inferior, weak positions representing the dark. The bottom and top lines depict what is outside of the situation. The lowest line is considered inferior in influence since it is only beginning to interact with circumstances.
The top line is considered to be of superior influence. It is the line of the wise man that has given up his worldly ambitions, and is about to leave the situation. It is the conclusion. The sixth line, the top line, will also often describe the outcome of the situation, if the proper path is not followed.
The second and fourth lines from the bottom represent administrators, women or sons. The fourth line being closer to the usual ruling line in the fifth position is regarded as superior to the second line. Because of its central position in the lower trigram, the second line has a close connection to the ruling fifth line, which holds the same position in the upper trigram.
The third and fifth lines are positions of authority and influence. The fifth line is usually regarded as the ruling line while the third line, being the top of the lower trigram, is considered the leaded of the masses.
Lines take on more importance when they are moving lines. These are indications of change and transformation.