This is not accurate. Everyone knew the Earth was round and had a good knowledge of the Earth's circumference, as this can be determined with geometry and some

This is not accurate. Everyone knew the Earth was round and had a good knowledge of the Earth's circumference, as this can be determined with geometry and some basic measurements. What was not well known at the time was the size of Asia, and specifically the distance from Asia's eastern coastline to Japan's easternmost islands, due to the lack of surveying data. Columbus grossly overestimated the size of Asia such that Japan would be approximately where North America actually is.