In order to answer the question you must first say what was the last discover that really changed how a map looks. To me there is two discovers that change how a map looks to the human eye. The first was the discovery of Bass Strait in 1800 and the full mapping of Alaska around the same time.

Here is a map from 1808 that has no major omissions unless you count Antartica and the North Pole.

http://www.worldmapsonline.com/images/1whistoricmaps/1w-wo-1808.jpg