Actually the Vikings are the same as the other Europeans in this case, although I think the Dutch are in the 3 pop category. I'm fairly sure the categories go as following, with letters being the first one in the civs name:
Ancient: E, I, C, B
Classical: G, P, C, R, J, E, M
Medieval: V, A, K, S, F, E, G, R
Later: D, M, P, I, M, A, T, A