In the 1400s, European explorers benefited from "improvements in map-making skills," since these allowed for greater location accuracy. GPS and steam ships would not be invented for quite some time.
The correct answer to this open question is the following.
Although the question is incomplete because it does not provide a specific reference about the author of the letter or any other reference, we can comment on the following.
A primary source is the piece of information that was written by a character or an individual that lived in the moment of the event, was part of the event, or witnessed the event. This individual could have written a letter, or a document -including a book. Or he/she took a photograph. Or was part of an interview. The secondary source includes information from a third person who was not part of the time or event but has found information through other resources. It is the case of an encyclopedia or researchers/historian books.
Wdym? What is ur question?
