The interesting thing about the Gwandongdo 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 on one island 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 is in the same book (Book 5) 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). 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.
In the geography section of the Annals of King Sejong in 1454, Ulleungdo was mentioned in the section describing Uljin-hyeon (蔚珍縣) as follows.
于山武陵二島在縣正東海中二島相去不遠 風日淸明則可望見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 to 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.
Both the "Gwandongdo" map and the Ulleungdo map came with attached notes, which are also shown below. The "Gwandongdo" map notes mentioned such things as the population of the region and the number of fields and paddies. The Ulleungdo map notes gave the size of the island and listed the flora and fauna found there.