What is the ruling on the science of geomancy (Ilm al-Raml) in Islam, and is it true that the Angel Gabriel brought it down to Prophet Idris and that it is an honorable science?

Drawing lines in the sand to reveal the unseen is forbidden because it is a type of divination (kahana), which is among the methods condemned by Islamic law. As for what is reported about Idris (peace be upon him) being the first to draw with a pen, this may refer to writing, astronomy, and mathematics. Astronomy is of two types: permissible (such as determining prayer times and the qibla) and forbidden (such as predicting events). The knowledge of Idris (peace be upon him) might have been of the permissible type, or it might have been permissible in his law but forbidden in ours. As for the Prophet's (peace and blessings be upon him) hadith: "There was a prophet among the prophets who would draw lines, so whoever's line matched his, then that is it," it means that if one of our lines were to match the line of that prophet, it would be permissible for him. However, there is no way for us to know with certainty if there is a match, and therefore it is forbidden.