Below is a map of Korea called "Corée" (Tyo Syen), which was produced by the French organization Mission Etrangères de Paris (MEP) in 1880. Supposedly, the map was based on Father Kim Degeon's Carte de la Corée of 1846. The map is said to be stored in the Research Foundation of Korean Church History.
Notice below the full map that there is a cutout of Ulleungdo (Oul-neung-to) that shows Ulleungdo's neighboring island of Jukdo (竹島) labelled as "Ou-san," which was the French pronunciation for Usan (于山). This map is more evidence that Usando (于山島) was Ulleungdo's neighboring island of Jukdo (竹島), not Liancourt Rocks (Dokdo/Takeshima).