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OED
definition: also "Charto-". The drawing of maps or
charts. 1859.
Introduction The concept of a map has been
with man for nearly as long as we have had the
ability to draw pictures. To be sure, the very
first maps were lines drawn in the dirt with a
stick. As man became more sophisticated, the use of
hide and later cloth and paper were used as a
medium for such drawings. But why must we have maps
in the first place? Maps help us identify who owns
the land, how many crops the land can produce,
where the dangerous shoals are, and many, many more
things. Maps also allow for goods to be traded
fairly over the world. Imagine a world where there
were some 250,000 different measures regulating the
flow of goods. It was a fact of life in France
before the Revolution in 1792. Before that time,
goods were measured by a set of standards kept in
the local grange, guild-hall, or town prefecture.
That's all fine and dandy for local trade, but each
town had its own set of standards that were
different from its neighbor. A very confusing
matter to be sure. Another problem is that of
distance. Just how far away is that town anyway? We
solve these problems by making and using maps in a
dizzying array of forms. Maps have been created and
used by many cultures throughout history. However,
the geodetic accuracy of these maps has varied very
widely, depending predominately on the customs and
traditions of the particular culture that made
them. The Chinese may have been the first culture
to formally make and use maps. The earliest
examples are thousands years before the birth of
Christ and show a remarkable degree of accuracy for
the time. On the other hand, maps made during the
Middle Ages in Europe (mostly made by members of
the clergy) show an equally amazing lack of realism
for the world they portray. Since the time of the
Reformation and the Age of Enlightenment, maps have
come to represent the land we live upon, the water
we drink and the very air we breathe. Actually, land surveys come
in two flavors: local land (plat) definitions and
in a grand form called geodesia, or geodetic,
surveys. Geodetic
Surveys Until
the age of global positioning devices, all land
surveys have depended on two critical ideas:
Astronomical observation and the twin mathematical
concepts of trigonometry and geometry. Astronomical
observation is vital because it allows the surveyor
to precisely locate any place on the globe. Even
during the middle of the Eighteenth Century, such
cities as Paris and London were accurately located
to within a few feet of their now known GPS
positions. Once the surveyor has two such places
identified, the distance between them can be
determined. Geometry states that if you know any
three parts of a triangle (two sides & an angle
or vice versa), the other parts can be calculated
using trigonometry. At the dawn of the the
Nineteenth century, all important surveys started
with two sites that were painstakingly located
using the stars. Each location was pinpointed by
repeated samplings of several stars, the North Pole
Star among them. Once the latitude and longitude of
these locations is known, the distance between them
is measured. Having established this baseline, the
real surveying thus began. from each of these
locations, the angles between a variety of
features, such as church steeples, mountain peaks,
etc., are taken and recorded. For the sake of
completeness and accuracy many of these recordings
are taken in both directions. from this data, the
distances can be derived because the length of the
baseline is already known. When this process was
undertaken on a grand scale for the first time (the
French Meridian (started in 1792) &endash; from
Dunkirk to Barcelona &endash; undertaken by
Jean-Baptiste-Joseph Delambre (1749-1822) and
Pierre-François-Andre Mechian (1744-1804) it
took seven years to complete. Perhaps the second
most important such survey was the The Great Arc
Survey of India which lasted more than fifty years
and ultimately located and determined the altitudes
of Mount Everest and her sister peaks of the
Himalayan Range. The Mason-Dixon Line (surveyed
1763-67 by two British astronomers, Charles Mason
and Jeremiah Dixon) is also one of the world's
first and most important geodetic surveys. The
error for its entire length of 244 miles is
estimated to be no more than one and one-half feet.
Land
Surveys Most land surveys we know
about and are familiar with -- those that define
the size of a farmer's field or where to put a
building -- are essentially the same process
undertaken by a geodetic traverse except that it is
done on a much smaller scale. In these cases, the
distances are measured in feet or at best a few
miles. traditionally, the surveyor started by
identifying two reference points and measuring the
distance between them using a Gunter's chain. Once
these reference points are placed, the angle for
each corner of the farmer's field was measured and
recorded in the surveyor's field book. Map
Making Taking measurements in the
field is only half of the story however. The second
important stage in the process of cartography is to
take the surveyors field notes and carefully
calculate the length of each leg in the survey.
Since a large survey may have several hundred of
these legs, the calculations may take days, weeks
or even months and must be verified by repeated
iterations. Only after these values have been
determined and verified can the actual drawing of a
map can occur. In essence, the draughtsman repeats
the process the surveyor used in miniature. Each
line must be placed on its starting point, measured
off precisely for both distance and angle.
Gradually, as these lines begin to intersect, the
lay of the land emerges. Although such a simple
drawing may be sufficient to to resolve a
territorial boundary dispute, most maps also
include a good deal more information, such as
populations, acreage, and other geographical,
sociological and cultural data. In essence, the art of making
maps is to create a graphical representation of the
world around us. So next time you pick up a map and
study it, take time to marvel at the amount of
information it provides in such a compact package.
It all seems to be so simple and yet amazingly
complex and represents enormous amounts of work.
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