Monday, August 18, 2008

Maps of Time and Tide.

Author: Seamus Dolly

Maps, for centuries have been the business of cartographers with mariners traditionally being able to make their own, in uncharted waters. Yes, the expression is still used in various contexts. I suppose that given the nature of open seas, one had little option but to find their own way. When a courier pigeon was the quickest communication device for help, an understanding of mapping was essential to evade Davy's Locker.

Land based cartographers were respected for their diligence and discipline that their trade required. Bench marking is another expression still used where a reference point is needed. It came from land surveyors and map makers. Particular heights above sea level were transferred inland, further and further, to give mappers some idea, as it couldn't be guessed with any accuracy otherwise. Indeed, twenty years ago, these benchmarks were heavily relied upon, where the presence of any other reference, was absent.

Now though, local authorities and surveyors use GPS or Global Positioning System. Even local civil engineers have access to this technology, and use it for projects such as small housing and commercial estates to anything bigger. So the traditional benchmarking system, which was little more than a ground anchored "pad" of stone or concrete, has already been replaced by something that can view an area in a larger relative context, a satellite.

A satellites' height above ground, or sea if you like, affords it a referencing advantage. There is no longer a need to physically walk to the sea (sea level), and determine levels, thereafter. The sea is water, to some degree, and while the earth is round also to some degree, water was "the great leveller". It has also been replaced by various liquids that are more visible, and have less tendency to obscure the inside of levelling chambers. Some have anti-freezing properties. You see, any accuracy relied on the visual clarity of the waters position within its' clear container, and of course the mappers understanding of parallax error. Parallax error is mainly a human one, where something is not viewed, correctly, or in cases like this, not viewed at 90 degrees exactly.

A photogrammetrist is a different version of a cartographer, and though their purpose is the same, their approach is different. They use aeroplanes in place of mountain boots, and indeed helicopters, which speed up the process. Indeed, some areas can only be practically mapped this way.

While the area of maps may have been considered to be boring to highly-strung teenagers, it is rapidly becoming a highly scientific and technically laden career.

There are still some sea floors that remain elusive or unexplored, mainly because they weren't of particular concern. They are so remote from a human perspective, that they warrant little examination. For now anyway, they don't interfere with sea or air navigation. If geologists can someway discover feasible mineral, oil or gas reserves, then commerce and necessity, perhaps, will induce a change in exploration priority.

To people that plan for contingency, local maps provide some clues to flooding susceptibilities that short term memories have forgotten. With global warming, this type of thing should be a consideration if you are planning your final or long-term home. In recent months within my area alone, the language of insurance companies suggests that they may decline their services, such is the climate change however subtle from a year to year basis, in combination with construction planning.

New construction projects have taken areas that historically, were flood plains, so where can the inevitable rains and their agreement with gravity, go? Within the home, is the answer.

To people that plan for contingency, somewhat extremely, those very same maps will offer guidance. Some dramatic predictions suggest that "a lump" of a particular volcanic island which is globally renowned for its' tourism, may slip into the sea. The same prediction suggests that it is being undermined by the sea, through corrosion. If this happens then a tsunami might demolish everything within fifty miles of seaboards.

It is a prediction, not a guarantee, like most future-related things.

One thing is more certain, perhaps, and that is that maps are essential, even if the medium which records them has changed from stone to parchment to disk.

About the author: Seamus Dolly is at www.CountControl.com

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