Clear Thinkers favorite Tory Gattis does the calculations and concludes in this post that the Texas Triangle Megalopolis — the area between Houston on the southeast edge to Dallas-Ft Worth on the northern tip down through Austin and to San Antoinio on the southwest edge — is the 10th largest economic mega-region in the world (and fifth largest in the U.S.) with $700 billion in GDP (based on 2000 numbers).