Why not add more information to the Tarot cards? (Tarot design)

Question: In the Minor Arcana of the Golden Dawn Tarot, we indicate the planet that sub-rules the decan on the card. Why do we not add the ruling planet of the sign on the card also? And why not the planet's dignity?

Answer: There is a concept in astrology called the "black chart" which is the result of adding more and more data points to the horoscope. For instance, you can add all the named asteroids, and all the Arabic points, and all the hypothetical planets, and all the fixed stars...and your chart will be completely black and overflowing with information--making it completely unusable. Sometimes, less is more. And for your average astrology student, the house markers and planets are about all they can cope with--it is the bare amount of information you need to read the chart.

Likewise, you could add all this other information to the cards...but each piece of information brings it closer to the black chart stage where there is simply just too much information. And in the case of exalted and fallen planets, that is specialty information--it is only useful if you worked with it a lot, or you have a handy chart. And honestly, the chart is far more useful than cluttering up the card itself.

Please note that both Adepts and astrologers are supposed to know the ruling planets of the signs. If you know the ruling planets, you know the falls; if you know the dignities, you know the detriments. (Basically, the negative weakened position is opposite of the strengthened position.)

Eight of Wands is assigned to the first decan of Sagittarius sub-ruled by Mercury. 

The information we put on the card is the bare minimum. So why the decan ruler? One, it is part of the base meaning of the card. Two, it saves you time figuring out what the decan sub-ruler is (I tend to have to count on my fingers to figure it out).

Whenever designing a Tarot card, you need to ask "Could I use this card in candlelight conditions?" If the answer is no, then you probably need to remove some clutter.