VI. The Twenty-Four Mountains: From the Eight Directions to a Fine-Grained Sitting and Facing

1. The Full Layout of the Twenty-Four Mountains

The full circle of three hundred sixty degrees is divided into the Twenty-Four Mountains, each spanning fifteen degrees. The northern Kan palace holds Ren, Zi, and Gui; the northeastern Gen palace holds Chou, Gen, and Yin; the eastern Zhen palace holds Jia, Mao, and Yi; the southeastern Xun palace holds Chen, Xun, and Si; the southern Li palace holds Bing, Wu, and Ding; the southwestern Kun palace holds Wei, Kun, and Shen; the western Dui palace holds Geng, You, and Xin; the northwestern Qian palace holds Xu, Qian, and Hai. It is made up jointly of the twelve earthly branches, eight of the heavenly stems, and the four corner trigrams Qian, Kun, Gen, and Xun.

For a shop, saying "sitting north, facing south" only reaches the level of the eight directions, and is not yet fine enough to plot a detailed Xuankong chart. Sitting Ren facing Bing, sitting Zi facing Wu, and sitting Gui facing Ding all belong to a north-sitting, south-facing shop, yet their yin-yang, the way the stars are started, and the judgment of a slant-facing (jianxiang) may all differ. Records must give both the degree reading and the name of the mountain and facing, for example "measured from outside the door looking in, sitting Zi facing Wu, the facing point near 182 degrees" — not simply "facing south."

Each fifteen-degree mountain further divides into a true facing, a slant facing, and a borderline zone. In practice one should never judge the facing by eye alone, nor force a reading into a particular mountain just to obtain a tidier chart. If a reading falls close to a boundary line, one should change position, remove magnetic interference, take repeated measurements, and record the range of fluctuation. A reading of exactly 180 degrees is not more auspicious than one of 179.5 degrees; the degree reading is first of all a factual datum, and only afterward a category in the divinatory arts.

2. How the Sitting and the Facing Are Determined

"Facing" (xiang) generally refers to the main side that receives qi and looks out toward the outside world; "sitting" (zuo) is the rear side, opposite the facing. A single-front street shop is usually oriented by its main shopfront and the side that continuously receives qi; a freestanding building can be judged by combining the main door, the lit face, the road, and the wall the building leans back against; a mall unit is more complicated — the direction the shop opening faces may be treated as the "small facing," and the mall's main entrance as the "large facing," and the two must be recorded on separate layers.

One should not mechanically take the direction the cashier happens to face as the shop's facing, nor always take "up" on the property deed's floor plan as north. Some units have two doors in equally regular use, and one must observe which door carries the main flow of people, the signage, the duration it stays open, and where transactions are actually initiated. If the front door stays closed for long stretches while a side door actually admits customers, the true qi mouth has already shifted; but whether the building's original orientation should be reclassified along with it is a further matter involving the conventions of different schools and the extent of renovation — the report should keep both pieces of data on record rather than hastily declaring that "the period and facing have both changed."

The judgment of sitting and facing can be drawn as a diagram of relations: "exterior incoming qi — shopfront opening — interior main axis — rear support." When the four agree, orienting the shop is straightforward; when they disagree, state the contradiction first. For example, if the door faces southeast, but the main corridor actually draws people in from due south, and there is no solid support at the rear either, then such a unit needs the door direction, the incoming route, and the interior axis examined separately — one cannot flatten all this information into a single arrow.

3. The Yin-Yang Grouping of the Twenty-Four Mountains

Starting a Xuankong chart requires the yin-yang of the mountain and facing to decide whether the stars fly forward or in reverse. Different plotting methods take the yin-yang of a mountain according to the Three-Cycle Dragon (sanyuan long) and the corresponding mountain, and it is not simply a matter of treating all heavenly stems as yang and all earthly branches as yin. When learning this, one must use one clearly stated set of plotting rules and a reliable reference table, checking the period star entering the center, the mountain-star and facing-star arriving at each position, and their yin-yang, before deciding the direction of flight.

A commercial report need not pile the client's copy with plotting jargon, but the internal record must be independently recomputable. At minimum it should preserve: the degree reading of sitting and facing, which mountain it falls on, whether it is a slant facing, the basis used for determining the period, the plotting convention used, and the numbers of the mountain-star and facing-star charts. If two surveyors using different software arrive at different charts, first check the true-solar-direction correction, the magnetic declination, the direction convention used for entering the sitting/facing, the forward-or-reverse of yin-yang, and the year of construction — rather than immediately blaming some secret of a particular school.

4. Slant Facings and Substitute Trigrams: Principles Only

When the sitting and facing deviate noticeably from a mountain's centerline and lean toward the neighboring mountain, traditional Xuankong has ways of handling this through the slant facing (jianxiang) and the substitute trigram (tigua). The exact thresholds for invoking these, and the substitute-star tables used, differ in convention across different lineages; this article gives only the governing principles: first, only discuss a slant facing once the reading has been confirmed stable; second, raise the level of re-measurement whenever the reading is near an empty-and-vanished (kongwang) zone or a sensitive degree-dividing line; third, never switch charts lightly over a one- or two-degree margin of error; fourth, if a substitute trigram is used, record the full table relied upon — it must never be applied on the spot merely to manufacture a more "flourishing" chart.

A substitute-trigram chart is not "a higher-grade auspicious chart" — it is an adjustment to how the stars are started, called for under a specific slant-facing condition. A true-facing chart, if the exterior form is sentient (youqing), need not be inferior to a substitute-trigram chart; a substitute-trigram chart, if the door and path are out of position, will not turn auspicious merely by its name. The worked examples later in this article mostly use true-facing teaching charts; where a slant facing is involved, they only show how to preserve the uncertainty, without inventing any secretly transmitted line-reading method.

5. Empty-and-Vanished, Straddling the Line, and Uncertainty

When a compass reading falls right near a mountain boundary or a trigram boundary, tradition often uses concepts such as "empty and vanished" (kongwang) and "straddling the line" (qixian) to flag that the qi there is mixed and impure. In practice, one must first rule out a false straddling reading caused by rebar, a door frame, an electrical box, a parked vehicle, or a phone's magnet. If the reading stabilizes once a few meters from the building, but jumps wildly right up against the door frame, that shows significant magnetic interference on site, and one must not draw a conclusion from whichever reading looks most dramatic.

Once it is confirmed that the building's true axis really does fall in a sensitive zone, the report should state plainly that "boundary uncertainty exists," lay out the neighboring conventions side by side for comparison, and give priority to whatever issue both charts point to in common. If both charts show that the entrance should be kept tidy and open, or that some particular spot should not be strongly disturbed, one can act on that shared point first; if the two conclusions flatly contradict each other, one should hold off on any major action and seek more reliable surveying data and re-measurement. The traditional arts, too, must honestly face the reality of measurement error.