prize7-2, Exercise 3: An error in the size of the Earth

Model answer (check the details):

A voyage plan converts a distance in degrees on the map into a distance in miles or days. If the Earth is smaller than assumed, then each degree is a shorter distance on the ground, and the same angular gap is a shorter voyage.

Example: if a geographer uses a circumference that is too small and also stretches Asia too far east, the sea west of Europe seems narrower than it is. A navigator trusting those numbers would expect to reach Asia after a much shorter voyage than the real one.

Consequences:
1. Supplies could run out before land.
2. A plan can seem reasonable only because of the error.
3. Disagreements between scholars about the size of the Earth were not academic but practical.

Link to the course: Chapter 4 returns to this argument about the width of the Atlantic before 1492.