I see in Japanese

I heard "そうか" a lot since I arrived in japan and I learned that "sou ka" means "I see" in english. This is very interesting as I also noticed that naruhodo "なるほど" can mean the same thing. These words are often used to show that you understood something and are very useful in basic Japanese communication. Apparently, そうか is more polite than なるほど. 

 In French or in english, the use is different because to mean we understand something, we use the word "seeing" which refers to the view. It's not the case in Japanese