Every circle is divided into three hundred and sixty degrees, and as the earth is round.

It follows that a circle drawn around it would be the same.

Each degree therefore means a distance at the equator of about seventy miles.

So unless whoever drew this map is positive that the island is exactly at the intersection of the degrees of latitude and longitude which you have given me, it might be seventy miles one way or the other off from the location given here.

And seventy miles is a good distance on the water.