Extremely rare first edition of Giovanni Domenico Cassini's landmark Planisphere, published in Paris by Jean Baptiste Nolin in 1696. (Other versions here ).

This rather self-evident observation [that the world could be measured and mapped based upon astronomical observations] was completely understood by the ancients who struggled with their limited technology to try to form from terrestrial and celestial data an accurate picture of the globe they inhabited. The closest to a modern calculation of the earth's size was achieved by the Greek philosopher Eratosthenes, who came within 14 percent of the correct circumference of the earth by measurements made in the Nile Valley and the relative angles of the sun's shadow at widely separated points along what was roughly the arc of a meridian.

Knowledge of the size of the earth was likewise bound up with the voyages of exploration in the 15th Century and earlier. It was in part due to rejection by Columbus of Eratosthenes' figures for those of Poseidonius. . . which postulated a globe roughly one-quarter too small, that the discoverer tried to reach the Indies by sailing west. In this, Columbus was only following a belief that was held by Claudius Ptolemy. . .

Cassini's map is one of the landmark accomplishments in modern cartographic history and represents a milestone in the transformation of the mapmakers art into the modern era. In his fine article on the Cassini map, Alexander Vietor states:

" The Cassini planisphere is assuredly one of the greatest cartographic landmarks connected with the furtherance of accurate map-making , and it is one of the first successful attempts to plot the shape of the earth from exact astronomical observations" —and numerous observations, judging from the map. Thus the ultimate desire of the ancient classical geographers for astonomical accuracy for place locations was at last achieved, at least in part, through Cassini's efforts.