Playing Korea, well: All your country is discovered and you wouldn’t actually need a map for liberating it 😉 Vice versa, knowing the terrain will facilitate conquering the Manchu, should you play China. Seeing the resources on the Samurai Invasion of Korea Map, will help you found cities in good positions and advance towards China and Korea quickly. Only the Manchu, merely emerging as a people at that time, can “still” (and have to) build cities. There’s no science and the major players Japan, Korea and China start with all cities built.
Thanks to several adjustments the Civilization 5 Scenario “Samurai Invasion of Korea” is a great scenario.