Consider China. I never grasped the point until I saw the place, but there is all the difference in the world between North China and South China. North is spare and austere, in some places virtually a steppe culture. South is damp and sticky, with swine flu.
It carries over into food. In America, we look for noodles and rice on the same menu. A moment's reflection in China will tell you that rice is south and noodles are north.
Or India. Here the fault line is linguistic: northerners speak mostly Sanskrit-based languages. The southern languages are Dravidian, which is about as different from Sanskrit as Hungarian is from Latin..
A particularly striking case (considering that it is so tiny) is Israel. "Biblical Israel"--in particular, Galilee, i.e., the north, can look verdant and fertile. Up in the corner at Dan, you find babbling brooks. The south--Judah--is spare and austere, plus the Dead Sea.
Which brings me back to the fajitas. I'm really inexcusably ignorant of Mexico, including its geography. Many years ago I did read Jack Womack's superbly readable biography of Zapata I got the sense Zapata's southern Mexico as a culture of small-holding farmers, in contrast to the cowboy culture of Pancho Villa's north.
Which brings me back to the fajitas: carcass singed on a piece of hot iron. Sure sounds like cowboy food to me. Good, though. But it makes me wonder: are fajitas specifically northern? And are there other parts of Mexican cuisine that are specifically southern. And is it part of our cultural chauvinism that we mash them all together on the same plate?
Update: A nanosecond after I posted this, I got this link from Joel, which probably answers my question. Also this,which also appears to be on topic.