I ran my own blog from November 2006 till October 2014. All posts are still online, but I don't have time to update it anymore. Please note that all images and media files have been removed when the backup was moved to a new host in early 2016. Enjoy!
The world map created by a man called Piri Reis in 1513 has become famous because of the the level of accuracy in positioning the continents which was unparalleled for its time - even maps drawn decades later did not have such accurate positioning and proportions. The map is also the oldest surviving map of Antarctica, despite being drawn more than 3 centuries before the official discovery of that continent. In 1528 Piri Reis drew a second world map, of which a small fragment showing Greenland and North America from Labrador and Newfoundland in the north to Florida, Cuba and parts of Central America in the south still survives.
Piri Reis, who's real name was Hadji Muhiddin Piri Ibn Hadji Mehmed, was an Ottoman-Turkish admiral and participated in multiple naval battles against Spanish, Genoese and Venetian navies ("Reis" is in fact a naval rank comparable to an admiral). Apparently he based his work on about 20 older maps he had collected, including maps personally created by Christopher Columbus. He collected his works in a book, which today has become one of the most famous premodern books of navigation.
The exceptional accuracy of his world map lead to many speculations regarding the origins of the maps he used to draw his world map, including claims that such accurate maps were impossible to have been created at this point of time. Some even believe the maps could be the remainders of older, yet unknown civilisations having access to higher developed technologies. Nevertheless, it seems that the exceptional quality of the Piri Reis map is the result of extensive studies and many hours of concentrated work.