Claudius Ptolemy (83 - 161 AD) is considered to be the father of cartography. A native of Alexandria living at the height of the Roman Empire, Ptolemy was renowned as a student of Astronomy and Geography. His work as an astronomer, as published in his Almagest, held considerable influence over western thought until Isaac Newton. His cartographic influence remains to this day. Ptolemy was the first to introduce projection techniques and to publish an atlas, the Geographiae. Ptolemy based his atlas on the "Geographiae" of Strabo, the cartographic materials assembled by Marinus of Tyre, and contemporary accounts provided by the many traders and navigators passing through Alexandria. Ptolemy's Geographiae was a ground breaking achievement far in advance of any known pre-existent cartography, however, it was not without flaws. In a masterstroke of ego that would last over 1,500 years, Ptolemy filled the many unknown and unexplored lands with mountains, lakes, and rivers that he merely assumed must exist. His other great error involved his use of the Cape Verde Islands as a Prime Meridian, thus wildly over estimating distances east of this point, and conversely underestimating the distances west. The ultimate result of this error was Columbus's fateful expedition to India in 1492. In any case, though the text of Ptolemy's Geographiae did survive, the maps that supposedly accompanied it did not. The earliest known Ptolemaic maps are in manuscript format and date to approximately 1300. Most of Ptolemaic maps that have come down to us today are based upon the 1477 Bologna edition of Ptolemy's Geographiae.