the mystery of the holes

Whenever I see any kind of natural phenomenon, I want to know how it happened, and why. A recent example has been the round holes that occur in mud banks in the local rivers, which I first noticed several months ago. The following photo, taken yesterday in the Shum Chun River on my way back from a journey to the west, shows how extensive this phenomenon is.

So how were these surprisingly regular holes in the mud of the river, each about 30cm in diameter, formed? I originally came up with two hypotheses, neither of which was even remotely convincing.

All the rivers in the northern New Territories have been canalized as a flood prevention measure, which means that the beds of the rivers were constructed using prefabricated concrete sections. And these concrete sections have neat rows of holes, each just slightly smaller than the holes in the mud. These holes remain full of water even when the river level is very low, making them ideal fishing holes for the local egrets, although it does appear, from passing observations, that this is the avian equivalent of shooting fish in a barrel. Unfortunately for my hypothesis, the holes in the mud are anything but regular in their spacing.

The second hypothesis centred on the notion of turbulence when the mud is underwater. The problem here is that it is impossible to imagine the kind of turbulence that would be required to produce so many holes, although one can imagine that the amount of water coming down the river for this to happen exceeds the design specifications of the flood defences.

It may be that the holes had always been filled with water whenever I saw them, so an obvious third hypothesis didn’t present itself: that the holes are the work of a horde of unknown creatures. This idea occurred to me only yesterday, when I saw the sandbank about 200 metres downstream from where the first photo was taken:

The holes at the water’s edge are filled with water, but those slightly higher are dry, and I was surprised to see that they are quite shallow. As can be seen in the photo, there is a small parapet of debris around each of the dry holes, which makes it highly likely that the holes were excavated. There is no sign of a burrow at the bottom of any of the holes, which would confirm the third hypothesis, so this photo is merely evidence, not proof. I suspect that crabs are the culprits, but this is just a guess at this stage.

You might wonder why I bother with such a trivial pursuit. After all, absolutely nothing of note hangs on solving this mystery. However, in an era of mobile communications, I prefer to pay attention to my environment, to listen to the sounds of nature rather than to a disembodied voice emanating from a smartphone, to look at whatever is happening in my immediate vicinity rather than at the screen of a mobile device. Unfortunately, my observations to date may have provided a mechanism for how these holes were formed, but I still don’t have any idea why. My best guess at the moment is that the holes are intended as a trap for potential prey, although I wouldn’t expect this to work if the holes are full of water.

optical illusion

When I worked in the Australian Outback in 1970, I used aerial photographs to assist my production of geological maps and the staking out of mineral claims on behalf of my company. When aerial photos are used for this purpose, it is customary for there to be an 80 percent overlap between adjacent shots. There are two reasons for this practice: to avoid the distortion that occurs close to the edge of such a photo; and to allow the viewer to look at the same point on the ground from two different angles.

The advantage of this last point may not be obvious, but consider that popular Victorian parlour toy the stereoscope. By looking at two slightly different images through a special viewer, the user could see a composite, three-dimensional picture. No one is going to lug a clunky wooden contraption around the bush, but small folding stereoscopes that will fit into a breast pocket have been around a long time.

And the resulting 3D pictures are remarkable. Trees stand out above their shadows, and small natural features are so easy to spot on the photos that it becomes straightforward to find wherever you are on them. However, there is an interesting phenomenon that happens occasionally, usually without warning. Trees and buildings become holes in the ground, and small hills become round hollows. This so-called ‘pseudoscopic’ image can be difficult to shake off when once seen, even though you know what the image should look like.

Which brings me to the point of this post. Last night, I was browsing through my folder of abstract photos when I experienced a similar phenomenon. I have the advantage of knowing the subject of the photo below, but for the purposes of this exercise let me just say that it is either a picture of pebbles on a beach or a kind of grating with irregularly distributed round holes in it. I could see only the incorrect interpretation, and I found it extremely difficult to force the optical processing system in my brain to switch images. However, the switch eventually took place automatically, and unexpectedly.

This is where you, the reader, come in. I hypothesize that each viewer will always see the same image first, that they will have difficulty switching to the alternative, and that this reflects how their brain is wired. Your assistance in either validating or refuting this hypothesis will be greatly appreciated. Please study the picture below before answering the following questions.

Which of the two images did you see first? Please record your answer in the poll on the right. Could you see both images? Did you have difficulty switching to the other image? Although this isn’t directly relevant to my inquiry, do you know what the real subject of this photograph is? I mention this because the origin of the round shapes is a mystery to me, and I have already disproved a couple of initially plausible hypotheses.

off the map

I have no doubt that Google employs some very clever people, but I am equally certain that none of its employees is a cartographer, having arrived at this conclusion because the company’s maps are the cartographic equivalent of a dog’s breakfast.

I’m not a cartographer either, but I do claim some expertise in the production and use of maps. When I sat GCE O-level geography, more than 50 years ago, part of the exam was a small section of an Ordnance Survey map on which we were asked questions, such as ‘Give five reasons why village X is located where it is’. This kind of question requires not only an ability to read a map but also an ability to interpret it, because a map with the richness of detail that is typical of Ordinance Survey products at all scales offers a vast amount of usable information.

Then, when I went to university, I spent a year studying cartography, which struck me as more interesting than the usual subsidiary subjects that are offered to science students. During this time, I learned how to use most standard surveying instruments, including a theodolite, a level and staff, and a plane table, to produce maps.

So what do I think are the principal shortcomings of Google’s maps? The way that roads are represented is hopelessly misleading: they make no distinction between dual and single carriageways, between single-track and two-track roads, and between metalled and unmetalled roads, although expressways are identified separately. There is also no indication of access restrictions, such as those that apply on many of the roads built by Hong Kong’s Drainage Services Department, which are gated to block access by motor vehicles and thus allow only pedestrians and cyclists to enter. Military barracks are not marked either, and a Google map that should include such a feature has roads inside the barracks that appear to be contiguous with roads outside.

The existence of footpaths is not recorded, even though there is an extensive network of concrete paths throughout the New Territories. And there is no indication of relief, apart from the occasional name attached to a prominent peak. This provides a clue as to why Google’s maps are of such poor quality. Clearly, they have been compiled directly from commercial satellite images, and information incorporated into a map is not verified by any system of checking on the ground.

There is also evidence that human input into the production process is either limited or nonexistent. Take a look at the satellite image corresponding to a map segment with a lot of roads. The ‘roads’ superimposed on that satellite image do not coincide precisely with the roads on the image. Not that a software-generated map is necessarily inferior to one produced by conventional means. The process of using stereoscopic pairs of aerial photographs to generate a relief map has been automated for more than 40 years, and the accuracy of the resulting map can be relied on.

Another absentee is a compass rose, which probably reflects the tendency among most users to hold their map so that north is at the top, regardless of the direction they are facing. This habit is inevitably encouraged by the presence of text labels on a map, which are most easily read if north is at the top. However, I once met two Ordnance Survey employees, who, to my surprise, brought a few examples of their organization’s maps with no text on them to the meeting. They too were surprised when I asked why such maps weren’t available for sale to the public, but there are many situations where text labels on maps are a distraction, and knowing what a particular landmark is called is of absolutely no importance when navigating across featureless terrain.

I do have some sympathy with Google’s position though, because in my experience most people are overwhelmed by the sheer quantity of information contained in an Ordinance Survey map, and for general use, not involving any detailed navigation, a pared-down product that includes only the most important information may be useful. However, that information needs to be accurate, or it is of no value.

Unfortunately, accuracy is not guaranteed. Here are two examples of egregious errors that I discovered in the process of exploring the northwest of the New Territories:

The red asterisk marks the correct position of the Hau Ku Shek Ancestral Hall (note the spelling error).

The bridge over the tributary of the Kam Tin River marked by the red asterisk does not exist, and the road actually follows the red dotted line. The footbridge about 100 metres upstream also does not exist.

Both mistakes could have been avoided by having someone checking on the ground, but this would have meant that the maps would have been more expensive to produce, and Google’s maps are a good example of a product that has been put together as cheaply as possible. As such, they have almost no practical value.

photographic abstraction #6

Welcome to the latest in my series featuring abstract photography; links to previous posts in the series are provided below. I am attempting to stimulate the individual viewer’s imagination with these photos, so I am interested in hearing what you think you see in the pictures. Also, based on what you see, you may want to suggest alternative titles. Cropping, altering the tonal balance and increasing the contrast have been used to produce images that are inspired by abstract expressionism, although none of the photos in this post resembles the work of any of the leading artists in this field.

other posts in this series
Photographic Abstraction
Photographic Abstraction #2
Photographic Abstraction #3
Photographic Abstraction #4
Photographic Abstraction #5

pulse

silent witness

poetry in motion

welcome to the machine

fractured