Ptolemy’s Geography

Ptolemy’s world map, circa 150 AD. Click to enlarge.

“Geography” (c. 150), or Γεωγραφικὴ Ὑφήγησις (Guide to Geography), by Claudius Ptolemy had everything you needed to make a world map, both instructions and data – and even the why of the instructions. It probably did not have an actual map – the text never refers to one. That was left as an exercise for the reader.

The “Geography” is why Westerners think of north as “up” and see the world as a grid of latitudes and longitudes.

And why Columbus thought he could sail west and reach Asia without running out of food and water: Ptolemy thought the Earth was round but much smaller than it is – and Asia wider (there was no good way to measure longitude till the 1700s). Columbus fudged the numbers even further in his favour – so that when he got to Cuba he was asking for directions to China!

Earth’s circumference: Ptolemy put it at 180,000 stades, 29% smaller than Erastosthenes’s 252,000. In Egypt, where they both lived, a stade was about 157.5 metres. That puts Ptolemy at 28,400 km, Erastothenes at 39,700 km. The correct value is 40,008 km.

Ptolemy was not original. Like his book on astronomy,  the “Almagest” (147), for the most part he was summarizing almost 2,000 years of Greek, Babylonian and Egyptian thought and research, putting it all together into one handy book. The idea of latitude and longitude, for example, came from Hipparchus in the -100s.

Ptolemy became the starting point for geography for:

• the Muslim world in the 800s, and
• the Western world in the 1400s.

In the West his book did not appear till 1397, in Florence from Constantinople, as part of the Renaissance, the rebirth of Greek and Roman learning. It was not translated into Latin till 1410. We can tell from the Latin translations that it took a while for Westerners to fully understand the book. In 1507, Martin Waldseemuller and Matthias Ringmann updated it as “Universalis Cosmographica” to include the geographical findings of Marco Polo, Columbus, Amerigo Vespucci and others – giving America its name along the way.

The “Geography” is mainly a list of over 8,000 places with their latitudes and longitudes. He even has Axum. His geography goes

• from the Fortunate Isles (Canary Islands) to Cattigara (Vietnam) 177 degrees to the east, and
• from Thule (an island north of Britain) at 63 degrees north, to Agisymba (Chad), 16 degrees south of the equator.

Londinium (London) he puts at 20 degrees east of the Fortunate Isles and 54 degrees north of the equator. The correct values are 18 east and 51.5 north. His numbers were approximate, some of his places mythical, but the mathematical foundation was solid.

Some strange geographical features:

• Taprobana (Sri Lanka) and the Golden Chersonese (Malaysia) are freakishly huge, especially compared to India.
• The Indian Ocean is landlocked.
• The Nile flows from the Mountains of the Moon (still on Western maps as late as 1851).
• The Caspian and Aral Seas are one.

Ptolemy knew about China but not Japan or the Pacific Ocean.

He knew what he did not know: that his map only covered about a fourth of the world – that the Western Hemisphere was missing and most of the Southern Hemisphere, that there were probably lands (and peoples) unknown.

– Abagond,  2021.

Sources: mainly “A History of the World in Twelve Maps” (2012) by Jerry Brotton.

See also:

• Ptolemy
  • al-Idrisi
  • Columbus
  • Amerigo Vespucci
  • Waldseemuller
• before Ptolemy:
  • Anaximander
  • Hecataeus
  • Herodotus
  • Euclid
  • Eratosthenes
  • Hipparchus
• latitude and longitude
• Axum
• Mercator
• 1851 in 12 maps

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