The interesting thing about the Gangwondo map is that Ulleungdo is shown with the label "鬱陵干山兩島" (울릉간산양도) which means "the two islands of Ulleung and Usan." (干山島 was a misspelling of 于山島.) The fact that both names were written as they were suggests that "Usan" (于山) was just a neighboring island of Ulleung island (鬱陵島) . We can assume that Ulleung was the larger island since it was written first. That assumption is confirmed by the Ulleungdo (鬱陵島 - 울릉도) map below, which was in the same book of the atlas and shows a small island off Ulleungdo's east shore labeled as "所謂 干山島" (소위 간산도), which means "the so-called Usando." Notice that the Ulleungdo map has the same spelling error (干山島) for "Usando" (于山島) as was on the Gangwondo map. Notice also that in addition to Usando, the Ulleungdo map shows five small islands off Ulleungdo's southern shore, which was a common feature of Korea's Ulleungdo maps. Similar maps can be found HERE.
In 1454, in the geography section of the "Annals of King Sejong" HERE, Ulleungdo was mentioned in the section describing Uljin-hyeon (蔚珍縣) as follows.
Korea uses the above passage to claim that Usan was "Dokdo" (Liancourt Rocks), and that the distance being talked about was the distance between Dokdo and Ulleungdo ("Muleung" was an alternate spelling for Ulleungdo), but Japan claims that the distance was a referrence to the distance between Uljin-hyeon and the two islands. The map below, which shows the two islands as just neighboring islands, supports the Japanese claim.
The two islands of Usan (于山) and Muleung (武陵) are in the sea due east of this hyeon. The distance between the two islands is close enough that they can be seen on a clear day when the wind is blowing.
By the way, notice in the above passage that Usan (于山) was written before Ulleung (鬱陵), which suggests that Usan was considered the larger island at the time the passage was written. That would explain why the old maps of Ulleungdo showed Usan to the west of Ulleungdo, instead of the east.
A product list for Ulleungdo is also listed below: