A stem mountain on the edge of two trigrams
Yi is the stem that closes Zhen. Its south line at 112.5 is not just the edge of a mountain but the edge of a trigram, where thunder gives way to wind. The trade is most careful on a trigram line: a stone reading 112 is turned back toward 105 before it is cut.
As a seat, Yi means sitting Yi and facing Xin: back to the east by south, front to the west by north. Yi also turns up as a water mark. Water coming in from the east by south is noted as water from Yi, and the master reads how it bends and where it leaves before the bearing counts.
Heaven's Office: a star that confirms and does not flatter
Yi carries Tianguan, Heaven's Office: duties, paperwork, administration. It is a common star, and Yi is neither one of the three auspicious nor one of the six elegant mountains, so it has no ranking to lean on.
Our school's rule is that a common star confirms what the form shows and adds nothing of its own. A guarding hill standing on Yi is judged as a hill first: is it rounded or broken, does it lean toward the site or away? If the hill is sound, Heaven's Office confirms a sound hill. If it is scarred or turned away, no star on the dial can turn it into a good one.
What this means on the ground
For a house, stand inside the front door, back to the door, and read outward three times with the luopan level and clear of steel. A door reading 97.5 to 112.5 faces Yi. For a grave, stand behind the stone and read along its face.
Inside Yi, the figures near 105 are the ones the trade likes. Readings of 98 or 99 lean on Mao, which is still Zhen, so the lean is mild. Readings of 110 to 112 lean on Chen, a different trigram and a different element, earth, and that lean is the one a master corrects.
Common mistakes
Confusing Yi with Mao is the commonest. Both are east, both are wood, both are Zhen, and a phone set to true north will put a Mao door on Yi in much of the world. Standing on the step facing the house gives the sitting, not the facing.
Setting a stone on 112 because it is still Yi ignores the trigram line two steps away. Reading Yi from a map or a satellite photo gives true bearings, which are the wrong kind. And taking Heaven's Office as a verdict about careers reads the star name as a fortune; it is a label, not a prediction.
Questions people ask
What direction is Yi on a feng shui compass?
Yi is east by south, 97.5 to 112.5 degrees on the luopan with 105 in the middle. Mao is on its north side and Chen on its south side. It is a stem, so it has no animal or hour.
What is the difference between Yi and Mao?
Mao is the branch at due east, 90 degrees; Yi is the stem just south of it at 105. Both are wood and both belong to Zhen, but a 15 degree swing moves a stone from one to the other, so measure, do not guess.
Is Yi a good sitting direction?
Sitting Yi facing Xin is a standard pairing on the luopan. Whether it suits a particular site depends on where the dragon enters and where the water leaves. A master walks the land first and reads the seat last.
Not sure whether your door is on Mao or Yi? Book a site reading and Master Zhang will set the seat to the degree.