Bertrand
The elemental associations I use are similar to the GD - probably for some similar reasons and some different reasons as I'm not really aware of GDs teachings, but simply because the GD propose this doesn't prove it is wrong or right.
There are several reasons which correlate those associations, but most of them are a bit hard to explain (and would probably don't make a lot of sense) in a written form on a forum.
Some are more obvious, for instance the earth/coins association is quite obvious because the coins are seen from above (the only suit for which this is the case), hence they are "on the ground", plus you can find clear geomantic figures within this suit, which isn't much the case for the other suits, then look at the Valet(page) of Denier underground coin which is another hint, etc... Then there are more "clues" one can experiment directly and physically - things that I won't try to explain here.
earth/denier, water/coupes, air/épées and fire/batons is what always worked best for me.
Regarding the purely numerological approach of numeral cards, I don't think it is a safe or valid way of reading them at first, as I detailled in this text
Numeral cards, an inner numerology
There are several reasons which correlate those associations, but most of them are a bit hard to explain (and would probably don't make a lot of sense) in a written form on a forum.
Some are more obvious, for instance the earth/coins association is quite obvious because the coins are seen from above (the only suit for which this is the case), hence they are "on the ground", plus you can find clear geomantic figures within this suit, which isn't much the case for the other suits, then look at the Valet(page) of Denier underground coin which is another hint, etc... Then there are more "clues" one can experiment directly and physically - things that I won't try to explain here.
earth/denier, water/coupes, air/épées and fire/batons is what always worked best for me.
Regarding the purely numerological approach of numeral cards, I don't think it is a safe or valid way of reading them at first, as I detailled in this text
Numeral cards, an inner numerology