How did ptolemy advance the field of cartography?

Ptolemy might rather be remembered for his contributions to geography than to astronomy. His maps of the world were so accurate for the time that they were used by scholars all over the world for centuries. Christopher Columbus based his theory of finding a westward route to India on Ptolemy's maps. Ptolemy's book Guide to Geography is often considered the beginning of the modern science of cartography, or mapmaking. The strength of the Guide to Geography is that in it, Ptolemy used the important system of latitude and longitude, the lines on a map that pinpoint certain locations, for the first time. The basic idea of latitude and longitude had been suggested by the Greek astronomer and geographer Eratosthenes 400 years before, but it was Ptolemy who developed a system detailed enough to be practical.The book lists the latitude and longitude of about 8,000 geographical locations known to the ancient world. Considering the simple tools and conflicting information Ptolemy had to work with, his maps are remarkably accurate.

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