Claudius Ptolemy (100–170 CE)
Ptolemy was a Roman astronomer, geographer and mathematician who lived in Alexandria in Roman Egypt. He is famous for writing numerous scientific treatises, most notably on astronomy (the most important being the Almagest), but his work the Geographia, an eight-book treatise, is also of huge importance.
He produced maps of the known world using geographical coordinates based on latitude measured from the equator (expressed as ‘climata’), with thirty-nine parallels from equator to pole, each interval representing fifteen minutes of daylight on the summer solstice. He calculated longitudes from a meridian in the west that passed through the Canary Islands. The Geographia, then, is mainly focused on the geometrical representation of geography. His guiding light was his precursor Marinos of Tyre (70–130 CE), and though his treatise was lost, Ptolemy used this as the basis for his work, and improved upon it, at the same time acknowledging the debt owed to Marinos. Ptolemy assumed the world to be a sphere (as had several predecessors) and estimated the circumference as 180,000 stadia – this made a degree of longitude at the equator some 500 stadia instead of the correct 600, i.e. he had underestimated.36 Ptolemy provided coordinates for 6,345 localities, which could then be placed on a grid to generate his maps; there is clearly excessive distortion in the east–west direction, with the length of the Mediterranean being overestimated in terms of degrees.37 The world maps were made with two of his three projections, and one is illustrated on p. 31, clearly a huge improvement over Strabo’s map. His world maps that would have accompanied the text are lost but were regenerated from his tables by monks during the Middle Ages. Local maps were part of Books VII and VIII. Ptolemy’s world maps proved to be the most accurate descriptors of the world until they were superseded in the fifteenth and sixteenth centuries during the Age of Discovery.More on the topic Claudius Ptolemy (100–170 CE):
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