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 ********************************* 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.