Alongside grammar and calligraphy, the Islamic world developed a body of speculation on the letters themselves, known as ilm al-huruf, the science of letters. It treats the letters as more than notation: as elements with numerical values, with assignments to the elements, the planets and the divine names, and with a place in accounts of how creation is ordered. Ibn Arabi, in the thirteenth century, gives the letters a substantial role in his metaphysics. Ahmad al-Buni, whose works circulated widely under his name and were much added to after his death, is the figure most associated with the practical and talismanic end of the same material.
The tradition is real, continuous and internally varied. It runs from speculative theology through Sufi cosmology to the making of squares, amulets and inscriptions, and its practitioners have included figures held in high regard and figures regarded with suspicion by their contemporaries. Jurists have objected to parts of it; other scholars have defended parts of it; the argument is old and is not settled.
The atlas records that this body of material exists, that it assigns letters numerical values through the abjad reckoning, and that it has a documented history and a documented range of positions taken about it. It does not set out the correspondences as a working system, does not supply instructions, and does not present the operative material as an available technique. Describing a tradition and teaching it are different acts, and the second is not what a reference work is for. Where a specific correspondence is genuinely attested in a named work, it can be recorded as that work's claim; where it is a modern reconstruction offered without attribution, it is not recorded at all.