I am referencing this from another blogger, which can be read here, who got the information from Wikipedia, which can be read here.
This Korean cartographer, Kim Jeong-ho (김정호) wanted to create an accurate map of Korea and so he literally walked the entire peninsula through mountains and across obstacles to do so. Upon completing the map, he gave it to the Korean regent (like a proxy king) Heungseon Daewongun (흥선대원군), who viewed as sensitive information that would clue foreign aggressors to Korean defenses. As the story goes, he subsequently had the hapless cartographer jailed and beaten. He eventually perished in prison.
One should note that this was a period of great foreign expansion into Asia, from the Opium Wars (鴉片戰爭) in China to Japan’s sudden expansion after the Meiji Restoration (明治維新-the line that produced Hirohito and is still the royal lineage). All of this effected Korea deeply, with encroachment from the Japanese, Chinese, French, Russians and even the Americans. The regent felt that this information could not afford to be put into general circulation so the motivation is clear. I am not sure if there weren’t alternative means of dealing with the issue that beating a mapmaker senseless, but who am I to judge?
The map is indeed impressive.