Theorem for # of colors for a map?

[duragezic]

Supposedly there is a theorem that determines the fewest number of colors needed to color ANY map if the rule is that no two countries with a common border have the same color.

I didn't think there was such a thing, but I guess there is. Does anyone just know the name of it? THanks.

 

[silverpig]

I don't know the name, but the number of colours you need is at most 4...

 

[mundania]

Four color theorem.. or Four color conjecture

 

[JayHu]

"Four colour theorem"
or
Every planar graph is 4-colourable.

proven by mathematical induction, and using computer verification.