This map is sort of an index of how much Europe knew about the world in 1502. You could almost date it to a particular set of months, because it reflects certain voyages but not others. It's like being back in the world of that time and getting an exact cross section of geographical knowledge.
Did the Portuguese change our view of the world?
In the 15th century the most accurate maps of the world were the ancient maps in Ptolemist geography, which actually dated from the second century A.D. They didn't go down to southern Africa because it wasn't believed to be inhabited, and they showed a land bridge from southern Africa to eastern Asia, as though the Indian Ocean were an enclosed sea. In maps from the later part of the 16th century, you can see that as soon as the Portuguese voyaged anywhere, information would come back. In an amazingly short amount of time you'd get a much more accurate view of the world. It was mostly coasts, because they didn't go very far inland, but they were careful about taking latitude readings, and they did the best they could with longitude, which is harder. It's quite amazing when you look at these maps to see these very vague contours rather quickly turning into the contours that you know from modern maps.