The story of a terrain that was supposed to have been backfilled, but only appears at night

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■ Contours that remain only at night

I first heard about this terrain when I was checking the margins of an old survey map. The drawing itself was a very standard urban redevelopment plan, with neat lines and annotations. However, there was one point that my eyes were inexplicably drawn to. It was a low-lying area marked as backfilled, a place that should have been completely leveled according to current official documents. Yet, the contour lines indicating the edges of that low-lying area remained faintly, like a draft that had been forgotten to be erased.
At first, I tried to dismiss it as mere printing unevenness or a quirk of the drafting process. But as I overlaid maps of different eras showing the same area, a strange commonality emerged. In every drawing, traces indicating that the place was 'once a depression' remained in some form. This is despite the fact that, according to official records, it was completely backfilled during large-scale construction over a decade ago and is now supposed to be developed as a residential area.
What bothered me even more was the talk about nighttime visibility. In the course of my investigation, I interviewed several people living in the vicinity, and two of them used almost the same phrasing. 'There is nothing there during the day,' and 'At night, I feel like it looks a little sunken.' They avoided further explanation, muddied their words, and jokingly changed the subject, but the way they fell silent was strangely uniform.
I myself have visited the site at night. The lighting is well-maintained, and the road surface is new. Even so, while walking, there was a point where the sensation under my feet changed for just a moment. It is not that there is a clear step. It is just that I can feel a faint slope, as if my body is anticipating a 'descent.' That sensation did not appear when I passed through the same place during the day. I still cannot judge whether what I felt was an illusion or something like a memory of the terrain.

■ Terrain that remains faintly in records

As I began to research the history of this area, I immediately noticed the scarcity of materials. Records from before the redevelopment are fragmentary, and for some reason, land ledgers and old photographs are often missing this particular section. Even though materials for the entire surrounding area are available, only the part corresponding to the low-lying area in question is blank, as if it had been cut out.
In old local histories, there is a sentence indicating that this place was once land where water easily collected. However, that description also lacks specificity and does not touch upon the reasons or circumstances. It only uses the vague expression that it was 'not a place to stay for long.'
I searched for even older maps. I checked everything, including copies kept by individuals and hand-drawn diagrams of unknown dates that could not be called official documents, but what was common there too was that this low-lying area seemed to have been 'intentionally ignored from a certain period.' The name disappeared, notes were omitted, and eventually, its very existence was removed from the premises. That process is proceeding far too quietly.
The accounts of the residents were similar. The older they were, the more they said they 'vaguely remember' the former terrain, but they would clam up when it came to specific events or reasons. 'I was told not to go near it at night,' 'When I was a child, I was warned not to cross the boundary.' Although such fragments gathered, no one would speak with conviction.
I have not yet been able to judge whether this terrain was intentionally forgotten or if it faded from memory naturally. However, it was certain that both the materials and the testimonies were blurred in the same direction. Land that looks flat during the day regains its contours slightly at night. I do not know if that phenomenon is a fact or an effect of memory. But if terrain is not unrelated to human perception, perhaps this place has not yet been completely 'backfilled.'

■ Inconsistencies remaining in the drawings

What I first recognized as a clear sense of discomfort was when I overlaid multiple urban planning maps. Even though they are supposed to show the same plot, the way the boundary lines are drawn does not subtly match. In the pre-redevelopment drawings, gentle curves are drawn along the edges of the low-lying area, whereas in the post-construction drawings, those curves are replaced by straight lines. Strangely, however, those straight lines do not perfectly mesh with the surrounding block lines. It looks as if it were intentionally simplified, but one cannot feel any trace of an attempt to achieve consistency.
What is even stranger is that the discrepancy is not corrected even when I check by changing the scale. Normally, errors are absorbed by scale or the omission of details. But only in this place, no matter what magnification I look at, it seems as if the lines are drawn on the 'premise that there was a depression there.' Although the process of backfilling should have been completed on the drawing, it seemed as if the subconscious of the draftsman could not completely erase the former terrain.

■ Missing plot numbers

The next thing I noticed was the blank space occurring in the sequence of plot numbers. While the surrounding blocks are numbered regularly, only the numbers corresponding to the area in question are missing from the preceding and following materials. Missing numbers themselves are not rare, but usually, the reason remains as a record. However, for this missing number, there was no note indicating the reason to be found anywhere.
I traced the past ledgers to confirm when the number was last used, but that record itself was ambiguous. It certainly existed in one fiscal year, and in the next fiscal year, it was treated as if it had never existed from the beginning. There are no traces of correction, nor are there any deletion lines. It is just arranged as if it had been blank from the start. That quiet way of disappearing was, if anything, unnatural.

■ Difference between nighttime observation and daytime records

In a way that cross-referenced with the testimonies of the residents, I organized my own observation records. In photos and videos taken during the day, the point in question looks the same height as its surroundings. The way shadows fall is natural, and there is almost no sense of discomfort. But when I checked the footage taken at night, I noticed that a slight distortion was occurring. The light from the illumination is interrupted as if it were sinking at a specific angle.
This could be considered a problem with the equipment, but the same phenomenon did not occur when I filmed other places under the same conditions. Furthermore, when I looked back at the acceleration data while walking, only at that point did the numerical values show a sway as if my body were being pulled downward. While it could be said to be within the margin of error as a numerical value, it was difficult to explain why there was a difference in the same place between day and night.

■ Overlap of recording times

Finally, I focused on the creation dates and times of various materials. Documents where important decisions regarding redevelopment were made, photos taken at the site, and reports indicating the completion of backfilling. I noticed that many of them were concentrated in the same time zone. It could be called a coincidence, but all of those time zones were after sunset.
It is not that there are no daytime records. It is just that documents indicating final confirmation or materials meaning 'completion' are created at night. It looks as if there was a need to process something that could not be determined during the day, during the night. I do not know if this coincidence has any meaning, but at the very least, I could no longer ignore the fact that 'decisions' regarding this terrain have always been made at night.

■ Nighttime surface observation

I visited the site several times at different times of the day and conducted observations under the same conditions as much as possible. Temperature, humidity, wind strength, lighting status. Even when I aligned those, only the impression of the surface changes at night. The paved road surface should be flat, but when I lowered my line of sight, there were moments when it looked slightly wavy.
Especially in positions away from directly under the streetlights, the edges of the light bend unnaturally. It is closer to say that the shadow sinks rather than that the shadow stretches. I kept my stride constant and passed at the same speed, but only at a certain point did the feeling of my soles touching the ground become ambiguous. It is not that the hardness changes. It is just that a sensation remains as if the next step is delayed.
There was also a difference in sound. At night, when the surroundings become quiet, there is a place where my own footsteps become smaller as if they were being absorbed for a moment. When I checked the recording, the sound pressure had indeed dropped slightly only in that section. I thought it might be a malfunction of the equipment, but it was not reproduced in records of walking in other places under the same conditions.

■ Sway in measurement logs

I took continuous data using simple measuring instruments. Almost no altitude difference is detected. Even so, in the nighttime logs, very small numerical sways are connected. It is recorded as vertical movement, but the amplitude was in a range that could also be taken as artificial movement.
However, what is strange is that the sway occurred at almost the same position every time. Even if I changed the day or shifted the time, the values would be disturbed near the same coordinates. That sway does not appear in the daytime logs. I do not have the words to explain that difference. It just felt as if, rather than the terrain itself, a 'terrain observed at night' exists.

■ Testimonies of surrounding residents

I interviewed three residents individually. All of them were people who had lived in this area for a long time.
The first person said that while taking a walk at night, 'the road feels a little long.' Even though the distance should not change, they feel it takes time to pass through that section. Since there is nothing there when they stop to check, they try to think it is just their imagination.
The second person spoke fragmentarily about memories from childhood. 'I was told not to go near there when it got dark.' They were not told the reason. They just say that only the feeling that there was something like a boundary remains.
The third person was more specific. When returning home late at night, they said there was a time when the placement of the streetlights looked different for one night. It was back to normal the next morning, and no record remained. But that night, they used the same expression, saying, 'I felt like the road had become a little lower.'

■ My own sense of discomfort

I have collected testimonies and checked logs, yet there is still no definitive evidence. However, every time I stand at the site, I am enveloped by the same sensation. There is a discrepancy between my understanding that this place has already been backfilled and should have nothing left, and the subtle information my body receives.
That discrepancy is not fear. Rather, it is closer to an unsettling silence, as if I am on the verge of remembering something. I do not know if a landscape that regains its contours at night truly exists. But the observations and testimonies I have collected are too similar in form to be dismissed as mere coincidence.

■ Overlapping Hypotheses

Faced with the materials and observation results I had gathered, several hypotheses emerged. However, none of them can be called definitive.
The first is the possibility that the underground structure has not completely stabilized even after the backfilling. Even if the surface is flat, subtle subsidence or stress imbalances might be occurring due to temperature differences and humidity changes at night, manifesting as a sensory sense of discomfort.
The second is the issue of human perception. The information that this was once a lowland is shared unconsciously, and under the condition of night, our senses compensate for it. The possibility that the darkness and silence are 'reminding' us of unevenness that does not exist cannot be denied.
The third is the idea that the inconsistencies in the records themselves are having an effect. Because the drawings and ledgers do not perfectly match, the judgment of those standing on-site wavers, and that wavering might be manifesting as a physical sensation.
As a fourth point, I hesitated slightly before considering the concept of the 'memory' of the terrain. It does not mean that the land retains its former shape. It is the idea that human activity and the consciousness of boundaries soak into a place over a long period, and only take on contours when the conditions are right. This is closer to a metaphor than an explanation.

■ Changes After Re-investigation

A few months after my initial investigation, I visited the same place again. To my surprise, the discomfort I had felt before seemed to have weakened. Even at night, the sensation of sinking was faint, and the fluctuations in the logs had become smaller.
On the other hand, there was a change in the materials. A copy of an old map kept by an individual had been altered with unfamiliar correction lines. The person says they haven't touched it, but the curves indicating the edges of the lowland have been redrawn to be smoother. As if it had been that way from the beginning.
I could have dismissed these changes as aging or a lapse in memory. However, the fact that the records seemed to be 'being tidied up' at the same time the discomfort on-site was fading bothered me deeply.

■ A Quiet Afterword

Recently, small-scale repair work was carried out in the surrounding area. Ostensibly, it was for pavement renewal, and no special reason was given. However, the scope of the work almost overlapped with the points where I had been continuing my observations.
After the construction, even when I walk the site at night, I hardly have the same sensation as before. When I ask the residents, more and more of them tilt their heads and say, 'Was there such a story?' Testimonies are decreasing, becoming ambiguous, and eventually, it stops being a topic of conversation.
Even so, I do not feel that it has been completely resolved. This is because the initial logs and notes from that time that I have in my possession are becoming subtly difficult to read when I look back at them now. It is not that the letters have faded. It is just that the meaning is hard to grasp.

■ The Never-ending Contour

Whether this terrain really only appeared at night, or whether our perception was just making it look that way, no conclusion has been reached. The fact that it was backfilled also remains unchanged officially.
However, I feel that the relationship between the records becoming complete as the local discomfort fades, and the records being rewritten as the site is tidied up, cannot be dismissed as a coincidence.
Perhaps being completely backfilled is not a physical process. It only becomes a 'place where nothing existed' when the contours disappear from both human memory and records. Was I just watching the middle of that process?
Even now, when I open a map, my gaze stops at that point. Nothing is drawn there. Still, I cannot help but feel that only the sensation of the night remembers the former depression.