Why were Columbus's measurements off?

• A. Overestimated How Far Marco Polo Traveled, Because Polo Never Measured Exactly.
• B. Underestimated The Size Of Earth.
• C. He Had No Idea Of Anything In The Way (Thought The Indies Were 3000 Miles Away: Really 12,500).
• D. They Were Perfectly Accurate.

Answer: (A)

Columbus based his westward plan on rough, secondhand reports rather than precise measurements. Marco Polo’s writings describe vast travels and distant lands, but they aren’t exact mile-by-mile measurements. Because Polo’s distances weren’t measured with precision, Columbus treated those figures as if they were exact, effectively overestimating how far Polo’s travels had taken him and how far away the Indies really were. That leads to the conclusion that Asia lay much closer by sailing west than it actually does, which is why his measurements came out off.

In contrast, while people sometimes point to Columbus underestimating the Earth’s size as a factor, the specific problem addressed here is the reliance on imprecise distances from Polo’s account.