North Africa and Iberia both have lots of mines available, making these cities insanely rich once they are upgraded. I'm playing Carthage, and NA/Iberia is definitely my economic center. Here's a list of North African and Iberian cities under my control and their income:

Gader 7600
Mastia 4600
Baikor 4500
Lixus 4000
Sala 3100
Sucum Murgi 3200
Sala 3100
Vellika 2800

Keep in mind, though, that these numbers come from a game where I control 49 provinces, and every city I own is fully upgraded economically, including full markets, mines at level 2, and all of those 36/60 turn large trading port upgrades completed.