Art Carlson wrote:-
snip
>For decades after Spanish colonies had been established in Mexico, they
>still believed the Pacific was only a third as big as it is. I don't
>understand this.
big snip
G.C. Dickinson in 'Maps & Air Photographs' pub. Edward Arnold, makes one or two
observations which may be of interest. I've scanned and OCR'd the first two
pages as below. (my steam powered OCR software is a little shaky on symbols so
please be tolerant of errors I haven't spotted.)
Tony Moss.
Diagrams omitted but available as GIFs
Just hit the Delete Key if it gets too boring! :-)
Tony Moss
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Chapter I
The Developing World Scene -
and Map Projections
The maps of our earth which we use today are better and more plentiful than at
any time in history : mapping and re-mapping proceed apace, standards
continually improve, and so well are we beginning to know our earth
(topographically at least) that we confidently expect maps of any part of it to
present much the same picture no matter what agency has produced them.
This has not always been so. Sixteenth-century maps of the world, for
example, differ very significantly one from another, and still further back in
time, when philosophy rather than fact had to fill enormous gaps in world
knowledge, an even greater diversity is found, Christian and Arab, Chinese,
Greek and Roman each envisaging the world in his own particular way. The
concern of these first three chapters is to relate how this ancient diversity
was transformed into modern uniformity and to emphasise some of the more
important obstacles which had to be overcome before this transformation could
occur.
Cartography in the Classical World
Although evidence of very early maps has been found in several parts of
the world the western or European School of map making undoubtedly had its
origins in the classical world of the ancient Greeks. As early as the fourth
century B.C. Greek philosophers and scholars, working through logical analysis
of known facts, were beginning to suspect the spherical nature of the earth ;
by the time another century had elapsed Eratosthenes of Cyrene, head of the
great Library of Alexandria, was able to make the first practical attempt to
measure its circumference. Like many another earth-measurer of later years
Eratosthenes' theoretical knowledge was much sounder than the crude instruments
with which he had to apply it, but even so his result - a circumference of
250,000 stadia ( about 28,000 miles) - was surprisingly good, and as later
centuries were to show, an established spherical earth measured to within 14%
of its true size was no mean achievement two hundred years before Chris!
t.
The Developing World Scene 3
But this was not Eratosthenes' only contribution to cartography. A
spherical earth needs spherical co-ordinates to define position upon it and it
is known that he also constructed a map of the classical world based upon what
today we should describe as seven meridians and seven parallels, including the
equator and the northern tropic. The map itself has not survived but
sufficiently detailed descriptions of it permit the reconstruction shown in
Fig. iA. When one considers its antiquity the known world around the
Mediterranean appears surprisingly well-shown and, as will become clear
shortly, even as a world map the result can favourably be compared with many
drawn a thousand years and more later.
Important though Eratosthenes' contributions to cartography may have
been, they were completely overshadowed three hundred years later by the magnum
opus of yet another Alexandrian Greek, Claudius Ptolemy (A.D. 90-168).
Published under the composite title of Geographia this remarkable eight-volume
work was essentially a description of the known world, but it included among
its contents a discussion of the theoretical and
practical considerations involved in making a map of the world, estimates
of the latitude and longitude of some eight thousand places, and instructions
for drawing twenty-six regional maps and two map projections. Unfortunately, no
original of any of Ptolemy's maps has survived, nor in fact is it certain
whether Ptolemy himself ever drew them, but we know from mediæval copies of
them that somebody did, and in all probability Ptolemy's one world and
twenty-six regional maps formed the first atlas. It was Ptolemy too who gave us
the names latitude and longitude, supplementing the former by climata
(latitudinal divisions based on the length of the longest day) and measuring
the latter from the legendary Fortunate Islands, the westernmost known land,
usually thought today to be the Canary group.
For reasons which will be explained shortly Ptolemy's maps were
enormously important in cartographic development. In the late fifteenth
century, one thousand three hundred years after their original publication,
they re-emerged, much copied, as one of the twin foundations of modern
cartography, and it is from one of these mediæval copies that the essential
features of Ptolemy's world map shown in Fig. I B have been taken. Coastlines,
rivers and mountains, at least around the Mediterranean and its nearer
neighbours, are well represented and with north at the top, the tropic almost
correctly placed at 23° 5 I' N., and converging meridians and curved parallels
imitating their global counterparts, Ptolemy's world map has a distinctly
modern look. The errors of the outer area, such as the enclosed Indian Ocean
and an enlarged Ceylon, are understandable enough but in one less obvious
respect there is a serious mistake - Ptolemy's earth is about a quarter too
small. By using Posid!
onius' estimate of the earth's circumference - I 8,000 miles, or I° equals
about 500 stadia instead of Eratosthenes' (better) I equals about 700 stadia -
Ptolemy translated his estimate of the combined length of Europe and Asia as
180° instead of the actual 130° ; it has been suggested many times that one of
the factors encouraging Columbus and the westward-sailing explorers may have
been Ptolemy's accidental 'narrowing' of the sea-gap between the Orient and
western Europe.
