The springer nature site is very useful because it contains maps that show the geography of many countries around the world and also the good information. But when I’m looking at the detail, I see that you indicate only ‘sea of Japan’, not both of ‘East sea’

From 37 B. C, world have been long used ‘East sea’ especially Korea. Also Korean have been used it in the home of life. It is also from the late 17th century West in the early 18th century, also on the map, renamed ‘East Sea’ or ‘Sea of Korea’. The map from England in 1721 also says 'EASTERN SEA'. But increasingly using the name ‘Sea of Japan’ is start at Japan since the mid-19th century. It’s the time when Japan ruled Korea as colony.

The naming issue of the sea is still controversial. I would appreciate your efforts to improve this a little bit and make it a more complete site.